Checkout some pics here of a GPS tracker we got to play with. This is nominally a vehicle tracker, but it could also be considered for other tracking applications. The unit is small and is powered from 12V. It draws up to 100mA. A regular SIM card is inserted. The unit has an external GPS antenna and a mobile phone antenna. It has a few other inputs and outputs too.
When power is applied, the unit is ready after about a 1 minute startup. When the number is called, the unit replies with a text message containing latitude and longitude as well as a Google maps link. Opening the link takes you to the location. If you would like to tinker with electronics or stuff like this, drop in to our regular Electronics, Microcontroller, IOT and CAD Evening every other Monday. Check the events section of our website for details.