Temperature sensor for fridge

Anyone know of a temperature sensor setup capable of living inside a refrigerator or freezer? Preferably without having to mod the refrigerator.

1-Wire device such as below from PCSensor.com works for my temperature controls, I use one of the USB interfaces on my Pi2 and have 6 sensors bought from various places working well on a PCSensor USB dongle. Bit of a pain to setup, but a search on here should show you how I managed it with plenty of help from other forum members. I’ve also got 4 others via 2 arduino’s that suffer the occasional dropout which I deal with in the rule. These control my Hot Water and Spa Pool, 2 sit at up to 75degrees and one sits at around 37degrees in spa water. I cabled them in Cat5 cable, and the USB powered one’s are more forgiving of extra cable and sensors than the 3.3V Arduino connected sensors.
The DS18B20 uses Maxim’s exclusive 1-Wire bus protocol that implements bus communication using one control signal.
•Unique 1-Wire® Interface Requires Only One Port Pin for Communication
• Each Device has a Unique 64-Bit Serial Code Stored in an On-Board ROM
• Multidrop Capability Simplifies Distributed Temperature-Sensing Applications
• Requires No External Components
• Can Be Powered from Data Line; Power Supply Range is 3.0V to 5.5V
• Measures Temperatures from -55°C to +125°C (-67°F to +257°F)
•±0.5°C Accuracy from -10°C to +85°C
•Thermometer Resolution is User Selectable from 9 to 12 Bits
•Converts Temperature to 12-Bit Digital Word in 750ms (Max)
•User-Definable Nonvolatile (NV) Alarm Settings
•Alarm Search Command Identifies and Addresses Devices Whose Temperature is Outside Programmed Limits (Temperature Alarm Condition)
•Available in 8-Pin SO (150 mils), 8-Pin SOP, and 3-Pin TO-92 Packages
• Software Compatible with the DS1822
•Applications Include Thermostatic Controls, Industrial Systems, Consumer Products, Thermometers, or Any Thermally Sensitive System

Thanks for the idea. I was definitely looking at the DS18B20 as a general sensor to use all over the place. I guess my main thing is how to wire it up inside the fridge. I guess it wouldn’t hurt the seals to run it around the edge and just let the door close on the wire?

Either that or tease it out via a cable entry for maybe the light if it has one. Be careful not to give any auto defrost drains somewhere for crumbs to collect, otherwise you’ll find pools of water forming.
My experience with the sensors has been really good once I got the USB dongle, I get a lot more misreads on Arduino and with Screened Cat6 than I do with the Pi and Normal Unscreened Cat5 Cable. You can also get fully plastic encapsulated sensors which is what I use for the pool and spa, with heatshrink over the top so the water has something to attack (take care not to get it too hot when shrinking)

I use DS18B20 in a waterproof case connected to Fibaro universal binary sensor FGBS01 (you can connect up to four of them).
I used normal security alarm four wire cable (about 12 m long), then getting below the door seal of the fridge with flex, flat ribbon cable covered by the silver duct tape. Second one is in the freezer. Connections were soldered.

Everything works fine.

Thanks for the ideas guys. I’ll have to test the flat cable around the door seal vs finding a “port” to push wire through.

Recently found this thread. Does anyone happen to know where to buy a Fibaro universal binary sensor in the US? I looked at a few sites which sell Fibaro products but they don’t seem to carry it.