There will be an oblong box at the back of the valve (inside the tyre) which is the transmitter. This box is an integral part of the valve. It's best to state it has TPMS to the actual tyre fitter (not the bloke that books it in but the bloke that does the work) as they can damage them dependant on how hairy a@@ed they are.
Also, make sure they all work before leaving the garage by letting air out and getting the display to flag the warning. That way, if they have caused a problem you can sort it there and then.