This is actually a transceiver. The ankle bracelet sends out an encrypted RF signal once every 25 seconds and waits for a reply from the device, so it tethers him to the device. The BlackBerry device does all of the tracking, all of the communication, all of the processing of rules. This is merely a tether to prevent the offender from walking away from his device.
On May 15th, 2012. See this statement in context.