Is 'Homing Beacon' technology possible?

In Spy Thrillers and superhero movies etc, there is often a scene where the only way the plot can progress is if the characters are following (or being followed by) a homing beacon.

They slap this little magnetic device on a car, and it flashes a little red light, then they have a little black box that displays a map and gives them a precise location of where to go.

Is that possible? In these days of GPS phones and fancy Star Trek-like gadgets made real, it seems like it should be theoretically possible to do something like that, but can we really?

These are called directional finders.

You can buy one for you car here or get a handheld device.

This is how radio tagged animals are tracked. I saw some guy on Animal Planet who was tracking snakes and he had this H shaped antenna. He explained that the front bar of the H was able to pick up a signal better than the back bar, and there was no signal from the sides. So that the signal strength varied with the direction you pointed the antenna. The snakes could be tracked by walking toward the direction of the signal. Each snake had a different frequency, by the way.

Hmm. So not quite at Star Trek levels, but essentially it is the same thing. Cool.

Those GPS tracking pods that they stick on the bottom of cars to track them… do they transmit a signal, or do you have to pick them up physically to get the track?

“Tick, I think you have to hide this on the villain first.”
“You mean… I have to find the fiend before I can use the Fiend Finder? What a ripoff!

[sub]sorry, couldn’t resist[/sub]

The H-shaped antenna will give you direction; with calibration for intensity, it could give you a rough idea of location on its own. You could place a pair of the H-antennae a known (smalll) distance apart to increase your precision, or place them a larger distance apart and look at where their directional lines cross. For example, if one points east and one points north, then it’s clear that there’s only one (nearby) place the Fiend can be. Lastly, you can use multiple “intensity-only” antennae to locate the Fiend, by drawing overlapping circles on a map. Two such receivers will narrow the Fiend’s location to two possible points; a third receiver that’s not collinear with the first two will pare your options to one. Additional receivers are overkill, but give you better precision.

A GPS receiver attached to the Fiend is nice, but it’s an unnecessary complication. If you gather the GPS data on-board a Fiend Finder, you have to transmit it from the Fiend (to the Hero) for it to be of any use. At that point, why not just transmit “beep beep beep” and use the above methods? The bonus here would be that you get data accurate to within 3m of your target, and your Hero doesn’t have to know his own location or even follow along. If your transmitter includes a pager or a phone instead of a radio, you could even SMS-Text message the location to an e-mail account. So there are advantages, but you pay for them in complexity. Unless you’re keeping a detailed log of the places your Fiend visits to build a court case, and intend to keep surveillance running continuously for days or weeks, adding GPS isn’t really worth it.

Another option is to passively home in on a known signal emanating from your Fiend (eliminating the need to place a bug). Using the “multiple intensity-only antennae” method from above is even more helpful when you realize that (a) such antennae already exist, and (b) most people carry around a transmitter keyed for these antennae anyway: cell phones! If your Fiend’s phone number is known, it is technically possible (although non-trivial) to compromise cell phone towers or enlist the aid of the phone companies to triangulate a phone’s location. With enough towers, you get triangulation that’s as good as the local cell network. No good in Iraq, but pretty good in the U.S., Europe, or Japan. “What if the phone is off?” you ask. I had heard that it used to be possible to activate parts of a cellular phone (like the microphone) remotely without the user’s knowledge. YMMV - I think you’d probably have to be a government agency or similarly well equipped (spy/right-wing conspiracy/black ops team/Batman) to pull this off.

I believe the only way to get a pretty little map with a nice big red moving dot is in the movies or using GPS (although I haven’t heard of a GPS tracker quite like that yet).

Cell phones can get you a general idea of where you are. Without a GPS phone, I could track a cell in between 2 cell towers and get a rough idea (within 500 feet) of where you are. With a map, I could figure where you were walking to for instance.

A GPS phone can trace someone within 50 feet.

I doubt you could get an accurate distance figure using a directional finder in a city…too many unknown objects in the way.

It’s not only possible, it’s rather common in urban settings. Lojack uses tiny radio transponders hidden in cars. If a car is reported stolen, and the car’s VIN is in the Lojack system database, the system broadcasts a code to the transponder to make it start transmitting its “homing” signal. Police cars and airplanes with Lojack receivers (easily identified by the four little antennas in a diamond pattern on the roof) can identify where the stolen car is and intercept it.

Close enough to sci-fi / spy-fi for you?

I hope the makers of the real life versions were smart enough to remove the flashing, beeping red light that’s so common in the movies. It always seemed to me that that was a dump feature to have on a covert device…

The Lojack unit I once saw actually installed a car looked just like any other dirty gray lump of a thing in the engine compartment. Naturally, if a car thief is really familiar with what’s what in the particular car they crave, they’ll be able to spot the device. So far, they’ve not been making Lojack devices disguised as actual components such as alternators or distributor caps. But they are silent.

As a side note, anybody driving a truck fully lined with copper screening is up to no good - screened trucks and buildings (ie: chop shops) are used to haul stolen cars and prevent the Lojack signals from getting out until it’s found and disabled.

I live down the street from a police station, and I see a few of the undercover cars sitting there with 4 of those little coil cell attennas in a cluster on the roof.

When I was working a field service job, we had vehicle tracking on the fleet of about 6 vans. The service manager or owner could tell where any van was at about one or two minute intervals. It would also tell information like how long the truck had been parked (useful for billing), present speed and total mileage during a period of time, say, a week to determine fuel economy.

There was a small gps dome and small, carphone-style antenna externally and a box with the guts under the dash. I remember hearing that after buying the equipment and the installation, it was about $30/month for the service. I looked it up when they were new and I think it used Nextel for tx’ing the coordinates and other info.

Us field techs didn’t care for the new oversight!

      • I like the idea of LoJack, but apparently the system it is based upon requires dedicated police radio equipment, and so it is only available in California.
  • If they made one based on a cellphone link instead of a dedicated radio I’d be interested, because then… I could get it where I live. When LoJack was developed cellphone coverage was pretty poor, but that has certainly changed. Cheap prepay cellphones cost perhaps $50 now and simple GPS receivers cost maybe $80…
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      • Well now I see that someone in Brooklyn has seen police cars with LoJack antennas, apparently. …I don’t have a clue where you can get LoJack, I have only heard of it being used in California.

  • To put it mildly, LoJack’s website SUCKS and has for a long time. They don’t seem to allow you to view a simple list of all the installers, so you enter your ZIP code, and if there’s none in your “area” you get no results at all. So I have no f***ing clue where the nearest place to me is to get it, or if it covers my area at all.
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The proposed E-911 service will be able to place cell phone calls into a much tighter radius, something like 2m IIRC.

Units which are integrated into the cellular system to provide minute by minute tracking are old hat now. LoJack is grossly obsolete technology.

A quick Google for [location tracking child] reveals lots of these devices, such as this one: http://www.gpsanywhere.com/gLocator.php

There are also dozens of similar systems available for vehicles, just google [location tracking truck]. Such as http://www.trackyourtruck.com/.
These are all essentially a modified cellphone with GPS that’s programmed to contact a central database to upload its current location every couple of minutes. Anyone with the right username and password can go to the company’s website and see exactly where the “phone” is now and has been.

So as long as the Fiend (or your teenager) stays within cellular range, you can follow their progress from any browser on Earth. Ain’t Progress great! (??)

It’s available places besides California. I have it and I’m in Atlanta. I think it is limited to major metropolitan areas though.

It came with my car and a technician from LoJack had to come out to my house to “activate” it but I don’t know what that involved. He really wasn’t that talkative about it. I did find out that there are about a dozen places in a car where they hide the transmitter and that they like factory installed versions because they can put them in places where its pretty much impossible to remove without taking half the car apart.

Lo-Jack has been in the Boston area for about 20 years. The first one I saw was welded to the frame of the undercarriage. The transmitters are deliberately not affixed in any specific location, though I imagine there are a limited number of suitable sites. I also think they were “fancier” about the installation and optional features in the early years. The actual function is probably better today.

Amateur radio enthusiasts (“hams”) have been conducting “fox and hound” transmitter tracking meets and games since before I was born. Some such contests were even held before WWII, and possibly before WWI. The Amateur Scientist column of Scientific American published complete instructions on how to make a sealed “watch battery powered” swallowable transmitter in the 1970s.

The signal power is often low, of course, and urban environments would not only shield the signal, but confound the triangulation with countless reflections.

In principle, it’s workable, as a practical matter… not really. Lo-jack was only practical because it had access to the car’s electrical system (possibly backed up by a decent internal battery to transmit for a limited time after the car battery was disconnected)

      • Well you see, the truck-tracking services charge you $ every month, to track where your truck is every so-many-minutes, and for your own car you don’t really need that. What you need is an integrated cellphone with GPS that mounts secretly on your car. If your car gets stolen, then you give your car’s “tracking phone number” to police, and they can call it and get its location as often as they need to. If you get my point, there’s no regular “service” involved, as such. You don’t need 24-hour tracking, you only want it when you need it. The only regular “cost” would be a fee for cellphone enabling, but it should be a pretty darn small fee, because 99.99%+ of the time you won’t use it at all.
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