Depending on your sensor setup they should be "sleeping" to conserve battery (if using battery). The sensors will only send messages when ordered to do so in code. The controller might send out ack signals depending on your setup but it is mostly in receive mode. On a side note if you are worried about RF interference it goes down to what frequency and what channel you are on as well as your settings for power. Also any other emitting device in your house could interfere. If you are worried about health issues you shouldn't be. You get orders of magnitude more EMF radiation from the sun than you could get from these devices.