If you're lucky enough to live somewhere warm like Florida, as I do, then you might already be enjoying some pool time. The rest of you shmucks living in more sensible climates are eagerly awaiting summer and the pleasant water temperature that it brings. Blake's parents have a pool and his kids have been asking every day if it is warm enough for swimming. To find out without making a trip to his parents' home each day, Blake built this remote pool temperature monitor . There are pool water temperature sensors on the market, but Blake's research showed that they often fail quickly due to the elements. He also wanted a system that was open, so that he could tailor it to fit his needs. This device does exactly that and was affordable to build. It is actually two separate devices: the sensor unit that floats in the pool and a separate display unit that shows Blake's kids the current water temperature. The latter is an off-the-shelf device made by Adafruit called the MagTag . It is a WiFi-connected 2.9" grayscale ePaper display intended for IoT applications. It pulls weather data and water temperature information from the Adafruit IO service via MQTT messages. The floating water temperature sensor is completely custom. Blake made that sensor's enclosure from PVC pipe, which is robust and virtually guaranteed to keep water out when properly sealed. That contains four major components: an ESP32 board, a DS18B20 temperature sensor, an 18650 lithium-ion battery cell, and a TP4056-based battery charging and protection board. A 3D-printed frame holds those components in place within the enclosure. The ESP32 connects to Blake's parents' wireless network and publishes temperature data to Adafruit IO, so the MagTag can retrieve the information. The device does need occasional recharging, but the ESP32 has a sleep mode that keeps power consumption down in-between temperature checks. With this setup, Blake's kids can glance at the MagTag read out whenever they want to find out if grandpa and grandma's pool is warm enough to warrant a visit.