The introduction of weapons and contraband into the correctional environment is an extremely serious problem. It places everyone's lives at risk... offenders as well as staff. You would be amazed at the items that can "fit" in various places - folding knives, cell phones, batteries, ammunition, small guns, drugs, etc. Here in Texas, back in the latter part of 2009, a 500-pound man concealed a gun in his fat folds - and IIRC he had been searched twice before it was discovered.
If you work in corrections or have loved ones that do then maintaining a safe working environment is at the top of everyone's list. Unfortunately, however, that isn't always possible.