Thermostats with dials, a lever or made before 2006 likely contain mercury.
Do you have an old thermostat at home with a dial or a lever that looks like the one pictured on the left? Then most likely you have a thermostat that contains mercury. Many thermostats manufactured before 2006 contain mercury. This thermostat is perfectly safe to use, as the mercury is usually contained in a glass tube. But if you decide to change your thermostat to a new digital or programmable model, disposing of the old thermostat should be done safely.
San Mateo County Environmental Health Services Blog 