Several months ago, I wrote about monitoring the refrigerator temperature with an inside/outside thermometer. With an inexpensive battery-powered unit, you can put a wireless “remote” sensor in the refrigerator and then see the temp without having to open the refrigerator.
That idea came from readers Jim and Barbara Shell. Now comes a further refinement from another reader, Bill Culbertson.
Bill uses a similar unit, but with one difference. Says Bill:
Even better, the unit I got keeps a min/max. So I can check to see how cold and how hot the fridge got since the last time I reset the min/max. This is helpful for fine tuning if I have the fridge at the right setting.
Also this is invaluable when I’m away from the marina to determine if a shore power outage or other problem caused the fridge to heat beyond food safe temperatures so I know to throw out something which isn’t safe to eat/drink anymore. I used to take perishables home after a weekend of boating because I couldn’t be certain they’d be good for our next outing if I left them on the boat. I don’t do that anymore. I just check the max on the galley unit upon arriving to confirm the perishables are ok and then reset the min/max.
What a great idea for anyone who isn’t aboard full time!
Our wireless thermometer has the min/max function but I’d never thought to use it this way. Of course, the model that we have — which has worked well for years — is no longer made. Two things that I know about wireless two-zone thermometers: (1) some work much better than others, and cost has nothing to do with how well it will work; and (2) you have to follow the instructions perfectly to get them set up (yes, you really have to open the instruction book). Also, many people complain that the humidity sensors on the less expensive units are not accurate — note that I’ve never really been looking for humidity info and so it didn’t bother me if it didn’t work well (in other words, all I cared about was the temp working well).
You can buy a wireless indoor/outdoor thermometer with a min/max at most hardware stores, home improvement stores and big box stores — make sure it has a min/max though if you want to use it as Bill does. But before buying one, check reviews (if you have a smartphone, you can Google standing in the store). Use lithium batteries for the longest life — they also do much better in the cold inside the refrigerator, so they are definitely best to use in the remote. Read more about various features in my original article but note that the thermometers I recommend there do not record the min/max.
Here are two wireless indoor/outdoor thermometers with min/max that are getting good reviews and aren’t too expensive (links go to Amazon):
Simplify meal prep on board with proven strategies for provisioning, maximizing fridge space, and cooking delicious meals aboard your boat.

Carolyn Shearlock has lived aboard full-time for 17 years, splitting her time between a Tayana 37 monohull and a Gemini 105 catamaran. She’s cruised over 14,000 miles, from Pacific Mexico and Central America to Florida and the Bahamas, gaining firsthand experience with the joys and challenges of life on the water.
Through The Boat Galley, Carolyn has helped thousands of people explore, prepare for, and enjoy life afloat. She shares her expertise as an instructor at Cruisers University, in leading boating publications, and through her bestselling book, The Boat Galley Cookbook. She is passionate about helping others embark on their liveaboard journey—making life on the water simpler, safer, and more enjoyable.
Cathy Winkler says
One caution – I had a wireless thermometer for outdoor temperature / weather prior to reading the original article and getting one for my fridge. Then I started running into issues with the fridge unit reading the remote for the outside, and vice versa. And the unit with the barometer was then telling me it was raining in my fridge :). So you may want to try different brands if you want one for outside and one for the fridge. Moving the remotes around didn’t seem to solve the problem. Finally went to a wired unit with the display mounted outside the fridge and the wire through the front door where it’s more out of the way.
Vala says
do you know if they will work in a freezer? is a freezer too cold for the sending battery?
Carolyn Shearlock says
Yep, they’ll work in a freezer. Mine that actually shows inside/outside temp has shown temps below zero. Be sure to use lithium batteries in the part that’s in the freezer though — they work at far lower temps than alkaline.
Dave Tew says
We keep our powerboat in the water during Maine winters. The enclosed ‘engine room’ has all the through hulls, etc. that would suffer from freezing so we keep an engine heater going. It turns on at 35 degrees and shuts off at 45. One of those min/max wireless thermometer sensors mounted in the space lets us know whether it gets below freezing. Now if only someone would come up with an inexpensive internet capable device that we could read from home or the car!!
Kathy Belanger-Barber says
Another great idea
Mike Poor says
The Ambient one is unavailable, but other products of theirs are available. I really like the 3 sensor package. 1 for ambient, one for fridge and one for freezer. Or, inside/outside/freezer. Thanks again
Marek says
We have this set up for years and have 2 separate sensors for the fridge and the freezer sections. We have to change the batteries every year is the sensors but so far this set u worked perfectly.
Mike says
There is a low tech way to monitor your freezer. Place a coin on a container of solid ice. If the coin is still on top of the ice when you return, everything stayed cold.
Carolyn Shearlock says
Many of our boats don’t have room for ice in the freezer!
Colin Leake says
Love it, so simple 🙂 Maybe use something like an old film canister if space is a problem.
Ted Arisaka says
Good idea to monitor temps. Our SeaFrost comes with digital displays, but we also record temperature data onto our N2K network with Maretron’s TMP100 unit. You can have 6 temperature probes. https://www.maretron.com/products/tmp100-temperature-monitor/
John S says
Curious of which Maretron temp probe you use in the fridge, the ring probe or the ambient probe with what looks like a black .75″ cover of some kind?
Allan says
I am a geek and sailor. I used a Raspberry PI single board computer with temperature probes to measure and track freezer, fridge and cabin temperature as well as compressor status and battery voltages. It also sends me an email whenever the bilge pump runs
Here is a link to my boat fridge
https://thingspeak.com/channels/657860