I am trying to make a prototype door sensor where a door stopper is activated when the door is opened and deactivated when the room key is present. This product would prevent people from having lock-outs.
1) I understand that there are XBee transmitters that could allow me to make my prototype. However, XBee transmitters have to be connected to Arduino Boards. This makes the transmitting device much bigger than the key itself.
Are there any standalone wireless transmitting device that does not have to be connected to an Arduino board and can communicate with a receiving device connected to an Arduino board on the door frame?
2) Are there magnetic sensors for Arduinos?