If your doing it yourself avoid insert a lever within 3" each side of the valve, IIRC when I fitted my TKCs the wheel has a sticker on it warnign about the sensor.
If yo are taking it to a tyre fitters, warn them about the sensors and show them where they are. Originally I was going to be lazy and have someone else fit the TKCs, and was going to insert a piece of card between the spokes with the sensor location written large for our local tyre centre "Engineer". I did it myself in the end. Very Cathartic. The neighbours will talk to me again, one day. I am sure ...