I got 2 sets of these, they are a reciver with LCD and 3 plug in transmitters - http://www.jaycar.co.nz/productView.asp?ID=MS6116 

Anyway, they are a totally irresponsible user of the 433MHz band with the way they work.

Every 6-7 seconds or so they transmit for a second, totally hogging the 433MHz band. To the point where my weather station sensors are not displaying most of the time, and it even takes a couple of trys to get other things to work. As my wireless IR repeater is also 433Mhz it means that most of the time is is blasting out a useless stream of data making remotes not operate too well.

I only just noticed this when I was trying to make another reciever for them to send the values out to cosm to get charted. They are transmitting any time the LED on the front is lit up. I thought that was just to show it was logging or something, not having close to a 20% duty cycle on its transmissions.