A key with a built-in light includes a blade, a mercury battery, a plate integrally formed with the blade having a recess with a conductive sheet in a bottom of the recess for receiving the mercury battery and a tongue extending over the recess but not in contact with the mercury battery when the battery...http://www.google.ca/patents/US5541817?utm_source=gb-gplus-sharePatent US5541817 - Key with a built-in light
