Working Based on existing GSM/GPRS network and GPS satellites, this product can locate and monitor any remote targets by SMS or internet.Free tracking with Google Earth, you no need to pay,no activation fee, no software use fee. * All that is requiried is a pre-paid GSM SIM card from AT&T or T-Mobile or any other GSM wireless provider(850/900/1800/1900mHz). 3G card can NOT be used * Simply insert a GSM sim card into the GPS unit. Whenever you call the unit it will respond with the coordinates of its location thru a SMS message. * You can then use these coordinates on any mapping software (for example google earth) which will show where exactly the unit is located