I use this
http://www.aliexpress.com/item/Waterproof-Real-Time-Car-GPS-Tracker-GSM-Vehicle-Tracker-Phone-SMS-Global-Locator-Anti-Theft-Car/32592111813.html?spm=2114.13010608.0.108.u5gVw9
hooked up to a 12v DC-DC converter.
I needed to buy a $5 prepay SIM card and top it up with credit to...