Munkees Small Compass and Thermometer Keychain is about 2.5 inches long without the keyring and about 4 inches including the keyring.  It weighs about 1 ounce.

Doubling as a compass and thermometer (reads Celsius & Fahrenheit), this keyring is great for camping, hiking, climbing, hunting, backpacking, survival and for your emergency kit

This keychain is very portable and can be put on your key ring, bag, purse, or pocket.