GPS Transmitter that works without Mobile Networks

Question

I need a device which can remotely tell me its location, either in realtime or with some delay. So, I naturally googled for GPS transmitters. The top product has much too large a thickness (I need it so that, it can be undetected through a few layers of cloth on both sides).

Then I thought of a small mobile phone, with which I would use Android Device Manager to locate. But problem is, internet connectivity is gonna be scarce. Nonexistent. So not that, either.

Here's my situation:

A group of objects is going to be delivered to a group of persons, by means of placing said objects in a large sack, or similar. I need to track this sack. Therefore, I must place in it a device that transmits to me its location. Since it needs to be undetected, it must be thin. Since networks will be nonexistent, it must report over some other long-distance network, or, alternatively, store a list of locations every [30 mins/hour/few hours] which are transmitted when it finally reaches network connectivity. This device must have a battery life of a few days.

That it be undetected is imperative. Should it be discovered, there will be loss of life. The bags may be similar to this or this.

So, is either my GPS or Mobile idea usable? If not, can you suggest anything?

Answer 1

I suggest the Light Bug.

It features:

• 8 day battery life
• Solar recharging
• Relatively small size (53 x 27 x 15mm)
• Transmission every 15 minutes
• Global satellite coverage (for GPS)
• Low weight (33 grams)

The only thing I have not managed to determine is what happens if it loses contact with cell towers. I don't know if it would log location data points and retroactively transmit them. However, I have a feeling you'll have a hard time getting anything better than that, without designing something custom from a custom chip.

It may theoretically be possible to flash your own software to the light bug, but I failed to find any information on that, and being a proprietary device, it is fairly doubtful.

Answer 2

If you are looking for a low-cost solution then I would recommend something like a teensy (cheap Arduino essentially with a lot of ram/flash) an XBee Series 2 63mW, an accelerometer, a GPS radio and a battery.

The XBee will transmit up to 2 miles in rural areas (line of sight) so you will have a large range to read data from the device. XBees are also mesh networking devices so you can set up routers to extend the range of your network. They can also be put to sleep to save power. The GPS radio and Arduino are self-explanatory, but the reason for the accelerometer is to save you have to constantly change batteries. If you are trying to track the bags being taken then you only need to track when they move, and accelerometers are a lot cheaper to poll than a GPS radio. You also might want to send a periodical ping back to your controller reporting battery power so you don't have to worry about a device being taken and having its battery die shortly after.