user7743: I am making a bike alarm for my bike. I haven't started yet.
Basically, I'm thinking of a pin to be connected to the metal post (to which the bike is locked.) I want to detect if that connection (to the ground via the metal post) is broken.
Is that possible?

user10794: How about fastening a wire to the post, and then the other end, on the bike, goes into a "jack" (the sort of thing you plug headphones into). With the wire inserted, it makes a connection, and the Arduino knows the wire is there. As the thief steals the bicycle the plug (or loose wire) is pulled from the jack, breaking the connection. i.e.


7743: <p>I am making a bike alarm for my bike. I haven't started yet.
Basically, I'm thinking of a pin to be connected to the metal post (to which the bike is locked.) I want to detect if that connection (to the ground via the metal post) is broken.
Is that possible?</p>
 10794: <p>How about fastening a wire to the post, and then the other end, on the bike, goes into a "jack" (the sort of thing you plug headphones into). With the wire inserted, it makes a connection, and the Arduino knows the wire is there. As the thief steals the bicycle the plug (or loose wire) is pulled from the jack, breaking the connection. i.e.</p>

<p><a href="https://i.stack.imgur.com/2z3Oe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2z3Oe.png" alt="Bicycle protection"></a></p>
