iPhone/iPad/iPod app to decode GMDSS transmissions
Remote weather stations, some car key fobs (although many in the US use 315 MHz), wireless grill thermometers, and many other devices use the 433.92 MHz ISM (Industrial, Scientific and Medical) band. Chances are good that if it is a wireless sensor, it uses this band.
Here is a waterfall showing transmissions observed here, using one of the inexpensive USB RTL DVB-TV Dongles:
The entire waterfall occupies 139 seconds.
You can observe several periodic transmissions. I have a remote weather station and a remote thermometer, so that accounts for two of them.
If you have an RTL tuner dongle, take a look and see what 433 MHz transmissions are occurring near you.