"Black boxes" were purchased in 2001 for use by the offender transport staff in order to prevent offenders from accessing the handcuff key slot or gaining leverage against the chain that connects the two wristcuffs. Since these devices were deployed, the transportation staff cannot recall any instance in which an offender has manipulated handcuffs. Another relatively inexpensive initiative was the purchase in 2002 of a nonstandard type of hinged handcuff whose shape and size of the closure arm allows the cuffs to lock securely around wrists both larger and smaller than those intended for standard cuffs; the heavy-duty hinges do not allow the same degree of leverage to be gained by an offender. Texas has also begun allowing its officers to carry chemical agents at all times while on duty. These carry-on-person chemical agents have been instrumental in preventing injury to staff and offenders on many occasions. Other technologies and devices that have helped improve staff and public safety are Adams hand-held metal detectors, body orifice security scanners, heartbeat detectors for use at the vehicle entry gate of a minimum-security facility, nonlethal electric fences, and body alarms for staff that enable them to summon assistance immediately.