Post by Cleve is incorrect

Cleveland says the ball is the alarm sensor. The ball must however be only pressed to activate the sensor. The sensor is in the castle. Enabling you can do against the brake disk, for example by pressing the ball.
I have secured with a lock and chain so my mountain bike in the basement because of this - was broken into before - including Raddiebstahl. Strikes me as currently viable and relatively secure solution. If someone is busy on the chain or on the lock hit the alarms (still got a second Alarm Lock: Abus Detecto 7000 RS1).
You can see the castles, at least with the thin, small MTB brake discs, enable any problems with your finger. Simply press against the ball. This should also be possible at the motorcycle. Do not know what dagegenspräche.
Once activated react both locks on movement with alarm. That should deter a thief.
He can drive even with the bikes, since the brake discs lock the wheels.