There's a bunch but a lot of them are going to have something like this plantower sensor: https://www.aliexpress.us/item/3256801607354554.html https://www.alie

There's a bunch but a lot of them are going to have something like this plantower sensor: https://www.aliexpress.us/item/3256801607354554.html https://www.aliexpress.us/item/3256801607354554.html It's a off the shelf part easily manufactured and possibly also easily calibrated. As a bonus you can hook it up to a Raspberry Pi or ESP32 board if you want.