It is a key with a key ring on it and a small snake chain attached to it the teeth of the key is self is a flat piece of metal.

This key can fit in any thing that could be considered a obstacle obstructing a way. This may be a door or a secret entrance. 
If its some thing like the latter the key can be pushed into said object until the teeth part of the key stops.
After this The key will start to make a ringing sound the closer it is to a item or person that can lift the obstruction like a key a lever or a person that knows the code to get in.
If there is no such thing the key will admit a screeching sound; because the obstacle is either permanently part of that place like a solid wall that can't be moved with a passage behind it with the owner who knew of it existence no longer alive or forgot about it or the ways to open it is not present in the dimension your on.
 

Notes: Detection, Utility, Exploration