# Smallest location tracker? **URL:** \ **Category:** Factual Questions\ **Created:** [December 18, 2020, 8:58pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362 "2020-12-18T20:58:51Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [December 18, 2020, 8:58pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/1 "2020-12-18T20:58:51Z")
In theory what are the size limits? Like in the movies when they inject it, using satellites. In the near future using current technologies we already understand. Let’s assume it is done by measuring timing to multiple satellites. No limit on cost. It’s operated by the CIA. No GPS receiver needed. Only a transmitter sending a brief ping. Must work thru single walls or a ceiling. What frequency band? Smaller than a watch battery? Any minimum size for antenna? Similar to dish network uplink? Any other possibilities besides satellite? It must work deep in the woods and indoors. So WiFi is out. 4g networks don’t have enough coverage. Eventually someone will come along with BLE? Seems trivial to make it nearly impossible to detect. Unlike Mission Impossible. I’ve designed a WiFi product that eventually cracks WEP, then phones home. This is different. Enough energy for 100 pings. Every hour or once a day. Would it be smaller if it could only ping twice? Thinking out loud. All in theory for an upcoming movie. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 18, 2020, 9:07pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/2 "2020-12-18T21:07:07Z")
> [@sbright33](#): > > Let’s assume it is done by measuring timing to multiple satellites…No GPS receiver needed. I don’t see how you envision this works without a GPS receiver. If the ping contains no information, all you can do is discern the nearby point that’s receiving the signal (cell tower, WiFi, whatever). I think any kind of extrinsic triangulation requires a lot of energy output. ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [December 18, 2020, 9:16pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/3 "2020-12-18T21:16:02Z")
Let’s do satellites unless you have another idea. Certainly you cannot triangulate by signal strength at these distances. An encoded ping with satellites measuring timing. Sort of like gps in reverse, to make it smaller. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 18, 2020, 9:20pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/4 "2020-12-18T21:20:34Z")
Perhaps I’m missing something, but I don’t understand what you mean by “do satellites” or “GPS in reverse”, if you don’t have a GPS chip. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 18, 2020, 9:26pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/5 "2020-12-18T21:26:51Z")
I’m assuming you mean rather than using extant, deployed infrastructure, there would be a network of satellites that would be listening for the ping and would triangulate? ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [December 18, 2020, 9:27pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/6 "2020-12-18T21:27:07Z")
No GPS chip in the tracker, to save size. It’s operated by a large government agency. They can modify or create their own satellite hardware. The size would be very large if the goal was to send location data up from GPS. Even GPS itself would not work with a CM’s sized antenna indoors. ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [December 18, 2020, 9:28pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/7 "2020-12-18T21:28:48Z")
Triangulate using timing ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 18, 2020, 9:30pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/8 "2020-12-18T21:30:00Z")
Does it have to work anywhere on Earth, because I think for this specific application, there’s going to be a break even point below which it’s more economical to deploy land-based antennae across the region where tracking is desired. or use drones to follow the signal or some such ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [December 18, 2020, 9:33pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/9 "2020-12-18T21:33:29Z")
That is correct and a very good point if you can follow the signal. Let’s assume it is blocked for a few hours, for many possible reasons. Therefore it could resurface in any nearby country. ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [December 18, 2020, 9:40pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/10 "2020-12-18T21:40:01Z")
In this case it could be very tiny indeed, with unlimited funding ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 18, 2020, 9:42pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/11 "2020-12-18T21:42:43Z")
If you want the device to be injectable, it’s going to have a very small power source, and from inside the body, it’s not going to transmit with enough power to be detectable by satellites. I might be out on a limb here, but I think I’m right in saying that transmitters designed to work from inside the human body need the antenna to be in the same room as the subject. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [December 18, 2020, 9:50pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/12 "2020-12-18T21:50:29Z")
What if you create a tiny transmitter that signals a drone using a tiny signal, and then the drone can have fewer constraints on size and detectability and broadcast its location? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 18, 2020, 10:00pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/13 "2020-12-18T22:00:10Z")
Maybe, but how long do you need this thing to work for? - assuming current technologies, you have competing constraints: 1. Small size 2. Long life 3. Long range If you want it small, you can’t have much range or longevity; if you want long life, it can’t be small; in fact out of those three attributes, you can really only pick one of them; out of the other two, one will be unsatisfactory and the other impossible ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [December 18, 2020, 10:04pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/14 "2020-12-18T22:04:23Z")
Could you build something to run on body heat? AND still keep it small enough to be stealthy? Probably not since you need surface area with heat differential to do this, and surface area means rapidly ballooning mass. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 18, 2020, 10:08pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/15 "2020-12-18T22:08:14Z")
Yeah, you’d need to run it on temperature difference, and the hardware to do that isn’t really tiny, so the subject would likely be aware of it. If you had access to the person’s shoes, you could build a piezoelectric generator together with the transmitter into the heel, which would charge the device when they walk - and that could be made to transmit over a fairly decent distance (although maybe still not to a satellite) ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [December 18, 2020, 10:12pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/16 "2020-12-18T22:12:06Z")
Actually, you gave me an idea - the device can just pulse your location every so often, rather than provide permanent tracking. So you could have something slowly build up charge until it has enough to send a broadcast. Maybe you could do something with heat differential that charges over a couple hours and transmits twice or four times a day? ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [December 19, 2020, 12:07am UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/17 "2020-12-19T00:07:03Z")
I like you’re thinking. It doesn’t take much energy for a short pulse. 100 pulses until the battery is dead. The problem is the transmitter and antenna size. I think it will be about the size of a pack of cigs? ---
**Author:** ![filmstar-en](https://avatars.discourse-cdn.com/v4/letter/f/50afbb/32.png) [@filmstar-en](https://boards.straightdope.com/u/filmstar-en)\ **Post date:** [December 19, 2020, 1:19am UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/18 "2020-12-19T01:19:07Z")
Wildlife trackers try to do a lot of this. It is a big market. Some track birds using GPS and satellite communications over vast distances. > **[Bird tracking — a masterclass](https://www.bto.org/understanding-birds/articles/bird-tracking-%E2%80%94-masterclass)** > > Phil Atkinson explains the technology behind tracking. Closer to home, here is a system for tracking pigeons. [![](https://img.youtube.com/vi/kiT_MZnB1X4/maxresdefault.jpg "SKYLEADER GPS Homing Racing Pigeon Ring 1st Test") ](https://www.youtube.com/watch?v=kiT_MZnB1X4) The technology has improved greatly in the past few years with an effort to make them smaller and lighter so they can be carried by smaller species without weighing the bird down too much. The professional equipment gets pricey…but so small and light! [https://celltracktech.com/catalog/](https://celltracktech.com/catalog/) I would not be surprised if there were amateur groups who develop the same electronic tech. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 19, 2020, 2:50pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/19 "2020-12-19T14:50:39Z")
I think you’re bogging down in defining the specs, instead of defining the task. What, exactly, do you want to be able to do? An example would be “Apprehend person of interest overnight, then release PoI and determine where in the world they go, with information at most two hours out of date, and location good to within a kilometer, without the PoI suspecting that they’re being tracked”. The problem would change if it needs to be updated more often, or to a larger acceptable error radius, or if they’re only going to be within the US or within a specific city, or if you can only run into the person on the street for a few seconds at the start, or whatever. Once we have the actual desired task, then we can decide whether we should try to use satellites or cell towers or dedicated terrestrially-deployed antennas or a truck with equipment on it or whatever. ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [December 19, 2020, 3:57pm UTC](https://boards.straightdope.com/t/smallest-location-tracker/928362/20 "2020-12-19T15:57:11Z")
The first thing I thought of is the ARGO system. You would have to design and build an extra small beacon, but the system tracks birds for example. > **[How Argos system works and how the Argos data is collected?](https://www.argos-system.org/using-argos/how-argos-works/)** > > The Argos system works through specific Argos transmitters, multiple satellites, terrestrial antennas and operational centres. [Next page](https://boards.straightdope.com/t/smallest-location-tracker/928362.md?page=2)