BALDR Pool Thermometer Floating Easy Read, Solar, Digital Display, IPX8 (Dark Blue)

A hand is a poor judge of cold water – after a few seconds, 50 °F and 60 °F feel much the same. For a gentle start that difference matters, and a thermometer settles it. This BALDR floats upright with a solar panel and an LCD on top and a sensor below the waterline. The maker gives a range of −4 to 122 °F (−20 to 50 °C), an accuracy of ±1.8 °F (±1 °C) and a first reading in about ten seconds.

It is rated IPX8 and charges itself from daylight, which suits a tub on a patio. A tub that stays under its lid or in a dark garage is a different case: the panel needs light, so keep the thermometer where it gets some between dips. It shows temperature only – timing the plunge is a job for a separate clock.

Tip: Stir the water before you read it and give the display a minute – still water settles into warmer and cooler layers.