Sensor to monitor your home server enviroment

[schoondoggy 771]

If you are only concerned about temperature, you can use a Multisensor. This could also monitor the door on a rack.:

https://shop.smartthings.com/#/products/smartsense-multi 

If you want to measure temperature and humidity:

http://www.amazon.com/Everspring-Z-Wave-Temperature-Humidity-Sensor/dp/B006T2H60U

This will monitor temperature, humidity, motion and light:

https://shop.smartthings.com/#/products/aeonlabs-multi