Nice, haven't thought of that. Good catch.

Oh, and there's always radio interference, too. A lot of handheld using in restaurants here in Austria used to use the ISM band. (Worth of note: For a lot of small establishments, the owners live upstairs in the house, with the restaurant is on the ground floor). You used to immediately know when the owner had a new baby, because the cheap chinese baby monitors would completely overwhelm the ISM band.

So, if it's a wireless keyboard, it's certainly a good idea to check if some new wireless gadget has been turned on (or an old one has started to malfunction).