Gate opener with bluetooth Answered

I wish to use a raspberry pi3 to detect when a paired smartphone in a vehicle comes in range to open a sliding gate. All the gate opening electronics is in situ.

What are the pros and cons of such an idea and are there any instructables already using this method. I noted an in/out board using bluetooth detection here. Also how many devices can be paired to a RP3.

I have not done any programing of a RP before.