This morse key is colloquially referred to as the Siemens key, although it was made by several different manufacturers. It has a bakelite hinged clamshell construction with a metal base and a rubber pad. The lid has a lightning bolt to warn of high voltage and the words "Vor dem Offnen Stecker Herausziehen" meaning "unplug before opening".
The base is marked "Baumuster T1 Anf. Z: Ln 26902", where "Baumster T1" means Type T1, "Anf. Z: Ln" which means this key was designed and used by the Luftnachrichtentruppen (Ln), the Airforce Signal Troops, and "26902" is a model designation.
Inside the key is a BAL stamp which is short for Bau Amt Luftwaffe, the Luftwaffe or air force approval stamp.
The key is in lovely condition complete with the original metal base and cable though not the termination plug and represents a very nice example of a scarce WW2 Luftwaffe morse key.