This page explains the JEMRF hardware and firmware

A wireless temperature sensor and wireless waterproof temperature sensor can also be used as a wireless switch, or a motion sensor, or a water sensor…and vice versa.

See below board schematic. There are connections for temperature sensor and button. Both can be use simultaneously without any firmware updates.

Board Layout

Convert your temperature sensor to multi-sensor

If you have a temperature (or waterproof temperature) sensor then you can connect an external switch to the button contact points on the board. You don’t need to make any configuration changes for the switch to work.

Convert your switch sensor to multi-sensor

If you have a wireless switch sensor, motion sensor, or water sensor then you can add a 10k thermistor and 1k resistor in the TMP and 1K positions on the board for temperature sensing. You will need to solder those two parts in place and also make configuration changes to put the device into a cyclic sleep mode so that the temperature is reported every INTVL minutes (refer sleep modes).