But if we can track them using these devices, they would likely also be detectable by the terrorists.
I say give them some guns!!!
Give them some way of defending themselves,,a couple of grenades, etc...
If the kidnappers know the contractors are armed,,,they may be less inclined to even approach them.
Do the terrorists have the technology?
Nope. First, the terrorists would have to have the equipment. Most of the guys catching and beheading folks are barely literate (Iraq continues to have a low literacy rate). Also, the transponder could operate on a classified frequency and use an encrypted transmission. The beheaders are barely literate thugs who are equipped with AK-47s and RPGs, not with elint equipment. These guys are different from the planners and implementors of the 9/11/2001 assault.