I travel a lot for work, and the easiest way to derail your plans is for your suitcase to disappear en route, so track it with GPS. This would be a good build for your viewers to attempt themselves as well, which I think are the best kinds of episodes and the ones that got me watching your show in the first place!
I'm thinking an Arduino with a GSM/SIM module, and a GPS module.
One solution would be to send an SMS to the device with instructions (where are you?), the device then waits until it has a good accuracy (maybe 30 seconds) and sends a return SMS with the lat/long. Possibly include speed and direction. You can enter the lat/long to Google Maps for graphical display.
A more complex solution is for the device to routinely update it's position to a web-based interface, which you can log in to and view historical track data as well as the current location. If the device is offline you could see it's last reported location & time.
Requirements:
- comply with dangerous goods requirements (particularly for the battery)
- automatically engage "airplane mode" for the GSM module and then return to normal when back on the ground (GPS speed trigger perhaps?)
- Long battery life (at least a few days - long enough for a bag to be located by the airline)
- Small size & lightweight
Thanks for your time, and keep up the great work with the show!