There is one location for a xBT I’ve been thinking about for a while, that would yield almost perfectly accurate temperature readings and wouldn’t require implantation in the traditional sense: the bladder. Push the chip up in there, and it should float around happily and be readable through the lower abdomen with a decently powerful reader - which the Halo is.
The reason I haven’t done it yet? I bet you anything the chip eventually will find its way down the drain hole, just above the prostate, thin end first, and block the flow of urine like a friggin’ bathtub stopper. That means an emergency trip to the hospital, and not tomorrow.
There would have to be a way to give the chip a shape that would prevent it from ever entering the urethra or blocking it in any way, but since it’s glass, it’s not gonna happen.