Fermometers are pretty cheap and they give you a decent idea of the temperature inside the fermenter but if you get them wet they are ruined and I always got mine wet. Then I found out about a non-contact infrared thermometer and while they are not as cheap, you only need one for however many fermenters you have and you can read the temperature from several feet away. As my vision gets worse, I find the nice big digital numbers easier to read too. Just stand back and use the laser pointer to show where you are taking the temperature, making sure it is above the water of the water bath and below the level of the beer and within seconds you have your temperature. They are also fun to use to determine other temperatures around the house and yard and can be used to indicate temperatures where you wouldn't want to put your hands, like next to a spinning pulley to indicate the bearing temperature. I got mine off Ebay for about $15 and it even came with battery included.
