With this parametric hoistway door release key you can unlock an elevator's hoistway doors in case of an emergency.
Be careful: Usually there's nothing behind the door but a deep hole.
Be sure to read some manual so you know what to do.
Triangle locks like these are more common in Europe than in the US.
For the States you'll need an elevator drop key usually.
Keys like these are defined in DIN-22417 and in German they are also known as: