I used the thc-268.
The below sensors are said to be compatible:
thgr-268
The transmitter can be placed anywhere that temperature and humidity monitoring
is necessary... garden, garage, baby's room, wine cellar, freezer, attic, greenhouse...
up to 120 feet (less through walls etc.) away.
Oregon Scientific Wireless indoor/outdoor monitors allow an additional three sensors.
thc-268
Oregon Scientific THC-268 Cable-Free Thermo Sensor with LCD Display and
waterproof probe. Monitor the pool, hot tub, pond, lake, heater or A/C Duct,
water pipes, and soil temperature remotely! Add up to three remote sensors.
thwr288a
One of a kind floating thermometer for the pool, hot tub, boat, lake,
or anywhere you want to know the temperature of the water.