They use conventional frequenies. Around here, the output is on 35.22 MHz and the input is on 154.600 MHz.
I have found it to be quite amazing how far away those "thingys" can be heard.
I have a friend who used to own several of the McDonalds around here. I told him about my ability to eavesdrop on the drive-thru window on my scanner. He said he used to park out of sight and use a scanner to check up on his workers.