DeeprBlu Floating Solar Pool Thermometer with Extra Large Backlit Display

The chiller’s app shows the set point; this shows the tub. The DeeprBlu is a light-blue float 6.5 in (16.5 cm) long with a square solar panel on top, a large LCD on the front and a white stem that reads the water about 5 in (13 cm) down. The listing gives a range of 32 to 158 °F (0–70 °C), an accuracy of ±0.5 °F as the maker’s figure, an IP68 rating and a backlight, and it ships with a string and one AA battery.

It is sold for pools, and cold plunges are not named anywhere on the listing, but the range covers them and a floating sensor does not care what it floats in. The two things it does not do are keep time and send the reading indoors. Tie it to the rim on the far side from the chiller’s return hose, so it reads the tub and not the freshly chilled stream.

Tip: In a garage the solar panel sees little light, so keep a spare AA battery with the towels – the listing does not say how long it runs on the battery alone.