Problem with Bluetooth read range for arduino project

Question

I have been working on an Arduino project for a door entry system in my business office but have encountered a problem.

I have a group of 8 working in my office but we have a room which only 3 members are allowed to enter. To stop unauthorised entry I have installed an Arduino door sensor with Bluetooth Low Energy (BLE) to the door which will always ring if the door is opened. The only way to stop the alarm from activating is for the 3 members to have their BLE fobs with them when they open the door.

The drawback I have found is that if I increase the read range of the sensor it picks up fobs which are nowhere near the door and the alarm never sounds. When I limit the read range to around 5 to 6 feet the fobs do not get read when they are put in handbags or wallets.

So I need a technology which can have a very short read range so it does not pick up fobs far from the door. I also need it to have a powerful signal within that desired 6 feet or less read range. The power of the signal should not be affected by being put in pockets, handbags etc.

It’s also important for mobile phones not to block the signals seeing as all my employees have them.

The technology should not rely on line of sight either because the fobs will be concealed in bags and wallets most of the time. Your advice will be most welcome and appreciated.

Answer 1

Why not simply check the RSSI of the BLE fobs while leaving the transmit power (range) at maximum? I'd add some logic to the firmware that sounds the alarm only if no "key-device"/BLE fob with an RSSI of greater than X is nearby.

Also you should probably check if your BLE scan-method has a concept of "slow" and "fast" scanning - meaning the intervals between each scan-packet. Higher frequency means faster detection.

A more common solution for access restriction would be to use NFC. The downside ofcourse is that the user needs to put his tag very close to the sensor, and it's not so easy to make it secure (non-copyable), as opposed to ready-made BLE solutions.