When I first started brewing I was using one of those “kitchen” meat thermometers that have a probe on a mesh-covered wire, and a digital display where you set the type of meat and the desired doneness. Very cheap-o, but it served me surprisingly well for years… in cooking, anyway.
It worked well for my first 1-2 brew days, but after that it just started going haywire, with the temperature jumping around seemingly at random. Since its whole point is to measure the temperature of moist foods, it never occurred to me that it might not be waterproof. So I guess now I know why it started going haywire.
I grew wary of finicky electronic gadgets so for the last several brew days I’ve been using the built-in kettle thermometer for monitoring of strike water temp and wort chilling, and a floating analog thermometer in the mash tun.
I suppose the moral of the story is I should just invest in a good-quality water resistant digital unit, rather than cheap crap.