I had bought a 'grab bag' of Arduino components, including some DS18s20 temperature sensors and NRF24L01+ transcievers. Aha - I can put these around my house and I'll always know the temperature everywhere.
I built a custom PCB (see photo) with slots for a Nano, the tranciever and a 3.3v power supply converter.
There's also (not shown) a "base station" with 3 8-digit LEDs that shows the temperature in each of 8 rooms in my house.
The code for the "base" station is at https://github.com/dplassgit/arduino/tree/trunk/thermo_base