Stick on to the fermenter vessel to gauge the vessel temperature instead of the room temperature. This thermometer sticker is great to identify which vessel is hot and which is not. Also, it prevents the over-chilling of your fermenter during the summer months by the accidental addition of too much ice. These stickers don’t require any battery, just normal room light to operate and can last forever (survive bucket washes usually last for 2-3 years).
LCD Thermometer Sticker