AcuRite Digital Wireless Fridge and Freezer Thermometer with Alarm, Max/Min Temperature for Home and Restaurants (00515M) 4.25" x 3.75"

tl;dr version: This works fantastic for monitoring a standalone freezer in the basement.Full story:We have a standup refrigerator-sized freezer in our basement (mainly because that was the only place in the house we had room for it). We've managed to leave the door cracked open a total of 3 times now in about 10 years, due to simple negligence, and have lost hundreds of dollars in spoiled frozen foods as a result. There's no reason this needs to ever happen, so after the last time a month or so ago, one part of my fix was that I wanted something to sound an alarm if the temperature rises too much.Enter this simple wireless temperature sensor. Since the use case here is for a single-chamber freezer, and our fridge is well out of range 1 1/2 floors above on the other side of the house, I opted to just put both sensors inside the freezer. One is on the top shelf of the door, theoretically the highest temperature inside the freezer and the first location to start thawing if the door were left open. The other is buried deep on the bottom shelf near the back, which is theoretically the coldest area of the freezer. This way I get an idea of the effective range of temperatures throughout the freezer at any point in time. In case anyone's curious, there seems to be a fairly consistent 15F degree difference between the two sensor locations, plus or minus a few degrees.Installing the batteries and connecting the sensors to the display unit was quick and effortless. I didn't have any lithium batteries on hand, so despite the freezer being below the optimal range for alkalines, I went with what I had and gave it a shot, knowing I could just go pick up some lithiums the next day if it didn't work. So far the sensors haven't had any battery issues despite the subzero temperatures.Placing the sensors inside the freezer was also easy, although I couldn't make use of either the suction cups due to the low temperature or the wire shelf straps due to the shelves being thoroughly encased in frost and ice. That said, having them just sit on the shelves seems to work fine. The display unit is magnetically stuck to the front of the door and has had zero issue so far with the signal from the sensors punching through the metal frame. Both sensors show a very strong signal indicator.I have not had an opportunity yet to test the alarm feature. I did reprogram the "refrigerator" sensor's alarm range to freezer settings and turned on the alarm for both. As pointed out in the manual, while one sensor is labeled as fridge and one as freezer, they're otherwise identical and you can adjust the alarm range for each one independently. You're also not limited to just cold temperatures - the nominal max is 158F/70C although the display only goes up to 99.9 in Fahrenheit mode - so you could easily monitor something other than a fridge and/or freezer with this if you wanted to. Anyway, one of these days I should probably take one sensor out of the freezer for a while and let it warm up just to confirm that the alarm is audible from another room.Overall, I'm very happy with this purchase, especially considering the reasonable price.

UPDATE !/16/25:Still working great!But I just wanted to tell you that I bought a second unit for the bedrooms so we can check temps from the living room. You can't use a second set because it picks up the sensors in the fridge and freezer, even though I have batteries in the two new sending units which are I the bedrooms.So I have been using the monitor in the living room to keep an eye on the fridge temps.But now one of my friends has had a few power outages, so I'm going to give the second set to her.I am so glad I got this item. Now I can track the temp of my fridge and freezer without opening the doors! It was a simple matter of inserting batteries and placing the sensors in place. I have the monitor on the side of my fridge via the 4 magnets, but you could also hang it on a nail with the hole on the back. The sensors take 2 AA batteries each, and the monitor takes 2 AAA batteries. I used regular alkaline batteries (Duracell). I opted to not pay for expensive lithium batteries. So far, I have had no problems. I had a power outage in the recent past, and would have liked to know what the inside temps were in my fridge (without opening the doors), so I would know when to go get ice. The suction cups did not work, the sensor units fell within seconds of placement. I did not clean the wall prior to placement, so that could be a factor, but I would rather have them sit on the shelf anyway. On the back of the monitor, you have a switch for Celcius or Fahrenheit, as well as a reset switch. I do not use the alarms. You have to program the alarm settings if you want to use them. You can reset the hi and low reading by simply pushing the "clr" button.*** UPDATE 9-26-17 ***I had a 10 hours power outage about a month ago. This acurite unit performed FLAWLESSLY! I monitored the fridge and freezer temps constantly, and when the temps got too low, we went out and got bags of ice so we could put all the food in an ice chest. Then I put the sending unit in the middle of the ice chest to make sure the temp remained low enough. I can't love this item anymore than I do right now! Worth every penny in my book.NOTE: I still have the same batteries in it, and they are still going strong. I do not use the alarm. But I do check the high and low temps every morning and then reset, and I check and reset at bedtime. My freezer temp ranges from -5 degrees (f) to 10 depending on how much we open the door. It does not seem to affect my Duracell alkaline batteries. Very happy I did not pay for lithium batteries.UPDATE 8-27-18: This unit is still going strong! I recently replaced all original batteries (at about 8 months in), even though they were working just fine. I wanted to make sure the batteries did not die when I had a power outage. This is the best unit.UPDATE: 11-15-23Still going strong! I can't tell you how many times this unit has helped during power outages. We don't turn the generator on until the fridge hits 40 degrees. We are constantly checking the temps day and night for piece of mind.I'm going to buy another set to measure for cold drafts in the bedroom. Two points of reference, one display.I'm amazed how many years we have had this, and it still works.