One US state reckons it's cracked how to keep track of all of its 44,000 prison inmates - RFID-chip them.

The Ohio Department of Rehabilitation and Correction (ODRH) has approved a $415,000 contract to trial the tracking technology with Alanco Technologies.

The pilot project will run at the Ross Correctional Facility in Chillicothe, Ohio. If all goes well, the technology could be rolled out to all of the state's inmates in 33 separate facilities. Inmates will wear "wristwatch-sized" transmitters that can detect if prisoners have been trying to remove them and send an alert to prison computers.

Staff will also wear the technology on their belts so they can be tracked for security purposes. Warders can activate an alarm themselves but the alert will also be sent if the transmitter is forcibly removed or the warder is knocked down.

Alanco claims system can pinpoint the location of staff and prisoners in real-time and track them within the confines of a prison.

The Ross project is not the first such rollout of tracking chips in US prisons. Facilities in Michigan, California and Illinois already employ the technology and Robert R. Kauffman, Alanco CEO, said he expects three new states to sign up to use RFID technology.