In countries which use electronic monitoring (EM), the devices comprise three functional parts.
The first is a transmitter device, which will be worn on the inmates' wrists or ankles.
The transmitter, which is shaped similarly to a watch, is resistant to water and vibrations. It is also sturdy enough to withstand sudden impacts and severe weather.
The second piece of equipment is a receiver unit installed at the inmates' house or other designated place. This receives a signal from the transmitter and relays it to a monitoring centre via mobile phone signals.
The last functional part is the monitoring centre and field management equipment, which receives the signal so police can check on convicts' whereabouts. Officers will know immediately when a convict violates a geographical or curfew restriction.
The EM devices can be located through Global Positioning System (GPS) and Location Verification Units, which allow authorities to track them to within 90m.