This product could be a nice solution for the city-bikes, and it doesn't need anything particular. Furthermore, you can use it on your old bike and you don't need to fear that the thieves steal it (as they would with an expensive electric bike left unattended).
"It is a unique product for the electric bicycles market. It is an all-included system which can be mounted on a bicycle in less than 1 minute without having to get Your hands dirty."
Here's the site of the producer and a video of Rubbee below.