An electronic key for a security system including an access control system and/or driving authorization control system, for a motor vehicle, with a housing within which electronics for wireless communication with the security system are disposed. The key further includes a holding compartment formed in the housing, wherein the holding compartment an energy storage device for supplying electrical energy to the electronics is located. A cover is releasably fastened on the housing and sealingly closes the holding compartment in an inserted position of the cover. The key further includes a slot formed on the housing for receiving a mechanical key. A mechanism is disposed within the slot such that the mechanism can be activated by moving the mechanical key within the slot, whereby detachment of the cover from the housing can be effected.