Eyes In the Back of Your Head

A Personal Radar System

By: Jim

By: Jim

Jim has a background in military aviation, specializing in combat rescue and close air support.  His opinions are his alone and do not reflect the policy or position of the Air Force or Department of Defense, and no references here should be interpreted as an endorsement of any product or service by any government agency.

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We aren’t big on “gear reviews” here at Tactical Tangents.  Partly because there are a lot of other outlets that will tell you which holster to buy or which pocket knife to avoid.  But every once in a while, if we come across an item that has the potential to change the tactical landscape, we have to tell you about it.  We will typically review it through the lens of People-Ideas-Hardware to help you place that hardware in context. 

Ever get that tingling sense that someone is coming up behind you?  We found a company that invented a personal security radar that could drastically limit an adversary’s ability to surprise you. That’s worth talking about.



Imagine four people – who have different jobs, function in different communities, and live in different environments…

A Sheriff’s Deputy in New Mexico, parked for a few minutes between calls.  In a parking lot, eating a gas station burrito and downing an energy drink while trying to catch up on reports.

An Air Force Security Forces Defender working sentry duty in a hasty defensive fighting position at a recently seized airfield in a combat zone. He and his buddy are taking turns looking out into the darkness through a shared PVS-14 night vision set and trying to keep each other awake with creative insults as they enter hour 16.

A Working Mom, taking a break from the kids while dad watches Spongebob with them so she can take a jog. She puts the earbuds in and rocks out as she works off that final few pounds from the last kid or gets ready to set a PR on her next marathon.

An Army Infantry Soldier on patrol at night along a tense and heavily guarded border.

These people all have certain things in common.  They are exposed to risk, they are already carrying enough stuff, they tend to be mentally and physically fatigued and on the backside of the human performance curve.  They may be task saturated or distracted by a myriad of attention hogs.

And now I want you to imagine a fifth person.  A man with ill intent, and a pistol, or an electric cord fashioned into a garotte, or a hunting knife – closing in behind those people and watching for an opportunity to kill or otherwise victimize them.

“21st Century Tactics”

At Tactical Tangents, we will always urge you to maintain situational awareness and a baseline level of alertness.  We want to make you difficult to surprise and hard to ambush. To us, that awareness is more important than what type of holster you use or whether you carry enough stuff with you in your “everyday carry” arrangement.



Action beats reaction.  The aggressor in an engagement will tend to have the advantage – they will have initiative and often a shock advantage.

Humans have a distinct anatomical blind spot.  It is so obvious that we tend to ignore it.  We are so comfortable in our role as omnivorous apex predators, that we forget our forward-facing eyes and relatively weak sense of hearing and smell (relative to prey animals) leave us with a distinct rear-aspect sensing blindspot between the 4 and 8 o’clock positions. That blindspot is mitigated when you are moving your head and body around, but it gets more distinct if you are stationary or focused straight ahead as most runners and bicyclists are.

He or she who detects and assesses the threat first stands a better chance of regaining the defensive advantage.  As we know from our study of action-reaction, and the bigger concept of Colonel Boyd’s O-O-D-A Loop, you have to see the threat, confirm the hostile intent, and figure out what to do about it in order to have any chance of mounting an effective defense.  The longer it takes you to detect and assess the threat – the greater your disadvantage.

Humans factors are no joke. As much as we want you to operate at or near 100%, we know that most people simply don’t work that way.  You are going to zone out, you are going to look down at your phone, you are going to get distracted, you are going to have lapses in your alertness and awareness– and it is absurd to pretend that you won’t.

So with those concepts in mind – there must be some way we can balance the risk back in our favor against that dirtbag coming up behind you.  Is there some technical or tactical solution to the fact you don’t have eyes in the back of your head?

Well yeah, you can literally have a buddy watching your back, and that is ideal. You could have some sort of aerial overwatch – but that costs money and takes attention even by itself.  There has to be some way to augment your situational awareness. Someone should invent like a radar you can stick in your back pocket.



Now for the exciting part.  So there I was, with my kids at a park near my house.  In the restroom, they had one of those boards with advertisements on it for various local businesses.  One of the ads was for “DefendSix” and it showed a woman running and the tagline “We’ve got your back.” As a student of personal security, I was curious but skeptical of what kind of snake oil this company was selling – so I googled them and saw that they are selling a sensor that joggers could run with, which would alert them if someone is coming up behind them.

Picture the scene of a woman jogging down a trail listening to her earbuds and oblivious to an attacker coming up from behind and dragging her into the bushes.  That is the scenario this system is meant to defeat.

Sounds simple.  Sounds too good to be true.  Sounds like snake oil. Someone has to have already invented this.  Someone has to have proven that it doesn’t work.

So I start digging in and trying to find out more.  There wasn’t much except for a couple of local news stories about it.  I looked for competing systems, and the closest I could find was a system from Garmin intended to help road bicyclists detect cars.  So as far as I can tell, this thing is new, and if it actually works – it might be a tactical game changer.  I contacted the company and arranged a meeting.

I met with Breanna, the DefendSix President, and Derek, the DefendSix Engineer.  They are a small operation and they are effectively self-funded.  They explained that this started when Breanna saw a news story about an Albuquerque woman on a jogging trail who was attacked and sexually assaulted – Breanna was talking to a friend from church about it – who happens to have a background engineering satellites for the Air Force about how she wished something could alert her if a bad guy was coming up behind her. They turned it into a project and fought through the design and development of a wearable radar. They got serious enough about it that Breanna left her job as a special education teacher to pursue this business, and they have patents pending.

They have two functioning prototypes, and I got to play with both of them.  Before I go any further, I need to caveat that I am reporting on a snapshot in time. They are in product development approaching design for manufacturing. So what I saw may not match what they ultimately field. This system is not available for sale yet.

The first thing you notice is that they are small and light – smaller than a cell phone, and about the weight of an empty cell phone case (though I expect that weight to go up some when they get the batteries sorted out).  The prototypes I saw are meant to work with an iPhone playing music based on her original concept, but also work directly with ear buds via a mini jack, and could be adapted to most radio earpieces.

Current Prototype. Smaller and lighter than a typical smartphone.

As you can imagine I had about a thousand questions, like:

Does the thing work? The prototypes I saw worked surprisingly well. Not perfectly by any means, but well.  I tried to sneak up on them, I tried to exploit cover, I tried to duck on my approach, I tried to rush them, I tried to approach slowly – and every time, the system detected me.  They do false alarm, but not as badly as I expected given the technology, and their engineer is in the process of optimizing the sensitivity against the false alarm rate.

Does the thing give you cancer or fry your reproductive bits? They don’t know for sure (pending tests) but assess that it puts out less energy than a cell phone. So right now, that is a solid “probably not.”

Does the thing stand up to abuse? The current version will handle a jogger fine, but they haven’t adapted it to combat applications yet.  They are still in the advanced prototype phase and have not yet produced a shock-hardened and tested version. My rough observation though, is that the thing is not much different from a cell phone – I wouldn’t want to drop it or land on it, but I didn’t feel a need to baby it.

Where do you put it? They found the best results are in the small of your lower back, you know, where you have that butterfly tattoo from Cancun.  Much lower, and you lose some effectiveness due to the movement of your hips and curvature of your tail section (which may aim the radar up or down in a sub-optimal way), but I stuck it in the back pocket of my jeans and it worked reasonably well.

Does the thing give you a million false alarms? Surprisingly no.  It does false alarm, but it works off of closure – so if you turn toward an object abruptly, you can trick it into thinking the object is closing in on you. But because the object has to have closure on you, the system doesn’t ping every time you pass a tree or parked car.

Is the thing ready for prime time? Not yet. In military-speak I would describe it as about halfway through developmental testing, and they do not yet have an operationally representative prototype to fully test.  They need to sort out manufacturing, they need to sort out the smart phone software, they need to do a lot more testing on everything from FCC compliance to whether it is going to give your kids a third eye or make them see the future.  In plain language, this system is not available to buy or use yet.

How is the battery life? They don’t have a final answer, but it looks pretty promising at over 12 hours on a charge.

How the hell does it see a person? Easy, people have a radar cross section, just like clouds and birds do.  The really cool part is they have this thing dialed in and have successfully detected people through walls.  That’s some video game heartbeat sensor stuff right there.

How does this handle the movement of a runner? Mostly pretty well.  It works on relative movement, so it is a lot more sensitive (longer range… out maybe 20+ meters) when stationary.  It gets less sensitive (shorter range, more like 7m) when running. But the bouncing doesn’t seem to impact it much.

How wide is its field of view? It pretty consistently picked up threats between my 4 and 8 o’clock positions. They quoted 120 degrees – which is roughly the same at that 4/8 o’clock wedge and the threats I really worry about are behind that line. Where that matters most is if you use this sensor in an off-body stationary application – like mounting it to a pole or wall. Field of view is a simple question, but the answer is complicated because of the nature of radar. If you want to nerd out, you can look up side lobes here.

Can I detect this thing with a car radar detector? Maybe.  They haven’t tested that, it doesn’t put out much energy relative to a traditional police radar, but it functions in a pretty common band.

Can it see a bear? They think so, but have not tested it.

How much does a personal radar cost? They don’t know, but they are trying to get the consumer retail one down to a $300 price point. That sounds like a lot of money, but I know a lot of women who wouldn’t carry a gun or even pepper spray, but would carry this.  And I know some cops who would buy it out of pocket for that peace of mind when they are parked. If they end up building a ruggedized military version, you can expect the cost on that version to rise substantially.

Is this going to encourage people to be lazy and complacent? It is an understandable concern – people tend to be lazy and complacent.  This system, particularly because it only sees closure and not just presence, does not replace situational awareness – it augments situational awareness.  It might buy you 1-3 seconds of warning time to detect, assess, and react to a threat. But that is more than you would have on your own. I assess that if you are prone to being lazy and complacent, this won’t change that but may prompt you to occasionally look up.  If you are prone to being alert and aware – this will give you an unfair advantage.

Will this tell me where the threat is, what he is holding, and what to do about him? No.  The alert is binary – if it detects closure by a human-sized target within its field of regard, then it will beep at you.


What this Means

This system has a way to go before it is ready for fielding – particularly to a combat environment, but it is distinctly promising.  Breanna and Derek are onto something. It has and will always have some limitations – it does not replace basic alert awareness. It will not see someone sitting stationary in the bushes. It will give some false alarms and it will have some failures to detect.  Those are inherent in the technology. But this is the closest thing I have ever seen to eyes in the back of your head, and it is a hell of a lot better than what we have now.

The rub here is that DefendSix is going to need more money before they have manufactured systems ready to sell. I’m not sure how they are going to do that – maybe through a grant or some kind of defense funding program, maybe through a crowdfunding campaign.  But I do know that for their investment so far – they have some really impressive prototypes that more people need to take a look at. I am not a financial advisor or investment expert, but it appears they have already overcome the highest risk technical challenges and now mostly need to get the smartphone app, a final operational prototype, a lot of testing and calibrating, and manufacturing completed. That is an encouraging level of technical maturity.  Similarly, I am not a military acquisitions expert, but if I worked at PEO Soldier, AFWERX, DARPA, AFSFC, or USSOCOM – I would at least be looking for a demo.

The challenge for us as tacticians and end users is to figure out whether and how to integrate this new technology.  If this sensor gets fielded in an effective and suitable form – does it mitigate enough risk to justify the weight and cost? I think so. Is there a particular criteria where a military, LE, or personal defender needs to consider it a desirable or even critical item?  How will it change our tactics, techniques, and procedures? Will it let us move faster? Will it let us tolerate other distracting technology that forces us to go “heads down?”  Do we need to adjust the geometry of a military patrol or police SWAT formation to take advantage of or maximize the effectiveness of the sensor? As threat actors become aware of this technology – how will it change their behavior? Could you see a sophisticated bad guy employing it against military or police? These questions lead us back into reassessing our people and ideas now that there is a major hardware development.


For more information, visit www.DefendSix.com or email info@defendsix.com

Full disclosure: Tactical Tangents does not have a commercial relationship with DefendSix.  They didn’t pay us to write this or to advertise them in any way. This widget is just really promising and someone needs to know about them. This article should not be interpreted as an endorsement in any form.

About the Author

Jim is a contributing editor in the Tactical Tangents project.  His background is in military aviation and close air support.  One of his goals in this project is to help his neighbors fight a regional uptick in crime in New Mexico.  The opinions expressed here are his alone and do not reflect the official policy or position of his or any other agency.  Any products mentioned or linked to are intended to aid the convenience of the audience and enable further research, and should not be interpreted as an endorsement by Jim, Tactical Tangents, or any other agency.

Tactical Tangents is a free online resource for professional development of the Public Safety, Armed Forces, and Self Defense communities, provided by PIH Tactics LLC. For further information, please visit TacticalTangents.com and follow us on Facebook.  We welcome your suggestions, if you have comments or corrections, please let us know.  If you found this article useful, please share it with your friends and neighbors.

About the Cover Photo

Vigilant warrior — prepared for anything”
WHITEMAN AIR FORCE BASE, Mo. — Airman 1st Class Arlando Budd, 509th Security Forces Squadron response force member, remains vigilant while providing close bound sentry for a B-2 Spirit Oct. 28. During this security detail, Budd must watch his area of responsibility to ensure unauthorized personnel don’t enter the zone. (U.S. Air Force photo/Senior Airman Nick Wilson) (Released)The appearance of U.S. Department of Defense (DoD) visual information does not imply or constitute DoD endorsement.


  1. Pete

    This is a solution to a problem the right people in my field have yet to realize exists; and I am thrilled to direct my peers to this article. I will personally be sharing this with the right people in my military career field.

    Excelelent find by Tactical Tangents and excellent work by DefendSex.

    • Brian

      Feature Idea: if the radar functions in a 360° span, even if it doesn’t, a screen that actually shows position instead of just a beep could prove more useful along with maybe a vibrate function instead of a noise. All and all however its great that someone is creating this…

  2. Joe Guerrero

    I want it.
    Lots of practical applications.
    Questions: Can it detect Chihuahuas, pit bulls, black cats or freaking pigeons or ravens or pesky nextdoor neighbors or suspected gang members?
    I’ll add it the my walking gear! My combat multi-tool, a fat belly knife, my especialty built fighting walking staff & my 1500 lum blinding flashlight!
    The killjoy is I’ve only been able to use this stuff 7 times since 2012!
    With this devise I can lie-in-wait!
    Remember Surprise, Speed & Firepower!