I am using the Vibrator electricity, but it gives only 2-3V so I have to up them for my 12V relay.
I use the sensor from a ball mouse to up the voltage, i think its called a omnitron, sorry my English ain't that good, but later I found 3V and 5V relays from my local electric store which trigger with 2-3V without a problem.
The phone is set to vibrate just once with a particular melody, so I let it ring once and close.