A handheld tracker uses a variety of technologies including GPS

Global Positioning System

The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 (Global Positioning System), GSM and GPRS

General Packet Radio Service

General packet radio service is a packet oriented mobile data service on the 2G and 3G cellular communication system's global system for mobile communications . GPRS was originally standardized by European Telecommunications Standards Institute in response to the earlier CDPD and i-mode...

 to enable companies and parents to track and communicate with their workers and children and elderly parents. Police can also monitor criminals under home detention.

Many of the Handheld Trackers available are small devices which will connect to a PC via a USB connection to enable charging of the unit and to set up the functioning of the feature buttons which can be used as emergency buttons which will send an SMS or GPRS communication of the GPS co-ordinates and perhaps open up a 2 way call using GSM so that a further assessment of the situation can be obtained. These co-ordinates can be used with Google Earth

Google Earth

Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...

to provide a free of charge tracking solution which will give a map or satellite view of the handheld tracker location.