This app sends GPG-verified requests over the internet to a given server. Currently there are the actions open and close, but request-type will be configurable. The request also includes a timestamp to verify the request is sent by the owner of the gpg-key and is not sent again by someone else. It is used in the ChaosChemnitz hackerspace in Germany to open and close the door without the need of a "real" key. You'll need https://f-droid.org/packages/org.thialfihar.android.apg or https://f-droid.org/packages/org.sufficientlysecure.keychain to sign requests.