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Nano-sized GPS Tracker December 11, 2012

Posted by louloizides in Mobility.


Impoverished and war-torn countries suffer from high kidnapping rates [1]. Secret GPS tracking devices that could aid in recovering these kidnapping victims are often part of science fiction plots, spy dramas and cop shows. A completely concealed GPS tracking device can help aid in the recovery of kidnap victims.



The current state of the art for a GPS tracking device is a small box that can be worn on an armband or kept in a pocket [2]. The problem with using this device in abduction situations is that the device would be found and confiscated very quickly. For a GPS tracking device to be completely concealed it would have to disguised as another object or hidden inside of the user’s body.

Hidden inside the body would be the preferred implementation of this device as it would be impossible to detect by the naked eye. There are two routes for accomplishing this – an implanted device and a device that could be swallowed. A device that can be swallowed is ideal for privacy concerns as the user could stay separated from the tracker and activate it as necessary.

For this implementation the device couldn’t be larger than the largest medicine pills available, size 00 which is approximately 0.8 inches in length and 0.3 inches in diameter [3]. Several other design considerations are required. Any device would need to allow the user to activate or deactivate it as necessary. For a tracker in a pill form, the device might be disposable and only activated once it’s swallowed. If a tracker were hidden in another object, however, the design would have to balance privacy considerations vs. the ability to activate it when the abductee might not be able to get to the device.

The type of networks available for a GPS tracker must also be considered. Cellular GSM, CDMA and LTE networks are obvious choices for such a device. But in kidnap prone areas such as Afghanistan and Somalia these networks might not always be available. So, a worthwhile device must either be capable of ad-hoc networking or sending out some type of a locator beacon.

For a GPS tracker to be useful location accuracy is an important consideration. A tracker’s location would have to be accurate enough for an abducted person to be located, and GPS positioning devices can lose accuracy indoors due to signal loss and multi-path propagation. The GPS tracker, therefore, would likely have to supplement its GPS position broadcast with another form of locator, such as the beacon previously described.

Data delay tolerance is extremely important for this type of device. The tracker won’t always be able to be connected to a network. It should buffer a reasonable amount of location data in case reliable connections aren’t available. In addition, location data should be able to be supplemented by movement data when necessary, such as a person’s change in speed and direction based on accelerometer readings. The buffer also allows data to be stored and sent to the server more efficiently in bursts rather than being sent instantly.

Of course, for all of the technical requirements, increasing the knowledge that such a device exists and is in use might actually make the most significant impact to safety by lowering abduction rates.


Privacy Concerns

Carrying a tracking device is a significant privacy risk itself. And the user of the device must have a reliable way to activate or deactivate it, while ensuring that the device couldn’t be activated or deactivated unintentionally.

The interface for obtaining tracking data should be extremely secure so that a person’s location isn’t used against them. Furthermore, having a buffer on the device also creates a privacy concern. Someone could potentially read a device’s buffer and find out where they have been. Both the tracking data and buffer, therefore, should be encrypted whenever possible. The designer of the tracking device must be able to balance encryption, privacy requirements, hardware requirements, battery life requirements and size constraints.


Current Art

Most GPS trackers today are worn in hidden clothing pockets or on armbands, where they can be easily found. Interest in creating a device small enough to be swallowed does exist. One inventor has already patented an ingestible GPS tracking device (patent no. US7554452 [4]). The device, however, does not appear to exist and the inventor is likely a patent troll. Additionally, a company in Mexico, Xega, produces implantable tracking devices to help combat kidnappings. But these devices are RFID tags and would become useless if separated from an external GPS tracker [5].


Ideal Design

At the least this device would have to have the following components:

1)     A cellular radio

2)     GPS chip

3)     A GPS antenna

4)     A CPU to process the data

5)     WIFI to supplement the cellular connection, provide location data and act as a beacon (optional)

6)     A memory buffer for delay tolerance (optional)

Producing this device in pill form is still outside of the realm of current technology. In order to build this tracker two key technological improvements have to happen. The size of the necessary components has to shrink significantly. Furthermore, long-term power sources need to be available to power these components.

Using power from a person’s body would be possible, but impractical. Pulling power from body heat would not work as the thermal converter would need both a cold and hot side to generate a current[6]. Another idea from the field of nanorobotics is to create a fuel cell using blood glucose and oxygen. Unfortunately, this combination only yields very small amounts of power, currently estimated in tens of pico watts [7]. Modern GPS chips require milli-watts of power – five orders of magnitude greater than what glucose fuel cells can currently provide.

Batteries used in hearing aids, however, have excellent energy densities. A size 13 hearing aid battery is 7.9 mm in diameter (slightly larger than the size 00 pill), 5.4 mm tall and provides 300 mAh of power at 1.4V10. This is enough capacity to provide a 50 mW 1.6V GPS chip with close to 36 hours of power if it updates its location for 10 minutes out of every hour [8].



A clear need exists for GPS tracking devices that can be completely concealed to counteract abductions and kidnappings. Because of companies like Xega, a market for combating abduction likely exists in countries like Mexico where the vast majority of the population is poor, but affluent citizens exist that can afford tracking.

It’s questionable whether or not the technology would be developed based on the demand of the application alone, but existing technology is on the verge of making a pill based GPS tracker a reality and current technological developments will likely create the required technology naturally.



  1. Dickenson, Elizabeth, “Kidnap Capital”, Foreign Policy Magazine Online, http://www.foreignpolicy.com/articles/2011/07/05/kidnap_capital
  2. Meitrack Press Release, “The Latest and Greatest in GPS Trackers-Introducing the MT90,” http://www.meitrack.net/about-meitrack/news/279-the-latest-and-greatest-in-gps-trackers-introducing-the-mt90
  3. Capsule Connection Capsule Sizing Information, http://www.capsuleconnection.com/capsules
  4. Cole, Gary, USPTO Patent US7554452, http://www.google.com/patents/US20050228268
  5. Purvis, Carlton, “GPS Implants May Be More Fiction Than Science,” Security Management, http://www.securitymanagement.com/news/implanted-gps-tracking-may-be-more-fiction-science-008954
  6. Leonov, V.   Torfs, T.   Fiorini, P.   Van Hoof, C., “Thermoelectric Converters of Human  Warmth for Self-Powered Wireless Sensor Nodes”, Sensors Journal, IEEE. Vol 7,  No 5. p.p: 650-657. May 2007.
  7. Hogg, Tad, “Chemical power for microscopic robots in capillaries,” Nanomedicine, 2 Oct 2009, http://www.nanomedicine.com/Papers/NanoPowerModel2010.pdf
  8. Duracell Size 13 Battery Specifications Sheet, http://www.duracell.com/media/en-US/pdf/gtcl/Product_Data_Sheet/NA_DATASHEETS/13.pdf


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