Vibrating batteries for GSM phones

It’s often the small, everyday things that turn out to have interesting features when you examine them more closely. In any case, here you can learn how vibration alarms and other mobile phone call annunciators work, and how GSM phone batteries are constructed.Maybe you’ve already wondered how a vibration alarm in a GSM phone actually works. Obviously, it must be small, but what else can you say about it? Want causes it to vibrate? An oscillating coil perhaps, or an oscillating armature? Or is it perhaps a miniature motor with an eccentric weight?Well, did you guess right? Figure 1 shows the secret of the vibrating battery: a tiny DC motor with a small weight attached to its shaft so that it is unbalanced when it rotates, and thus vibrates.