Door Sensor Alarm

So the background for this is I am a teacher, and I am looking for a way to prevent students from leaving my classroom with calculators in their hands. I have this idea, not sure how feasable, but it sounds simple enough.

I would like to have a door sensor that buzzes every time it senses a (lets call it a badge for lack of a better term) that is placed say under a sticker on the inside of the calculator battery door. Anytime the student passes near the door with the calculator it buzzes so that student remembers to return the calculator.

  1. which arduino sensor would be best suited for this project?

  2. what device/badge/(rfid maybe? too much?) should be used on the calculators?

I believe I can figure out the coding...I just need some terminology help and direction with hardware.

All and any help appreciated! :slight_smile:

Maybe look at this description and you'll see all the terminology and related items :

However, these are short range ones. For your application, you'll need a longer range.

So I "could" use RFID for shortish range (1-2ft) for a simple buzzer detection application?

unless your purpose is to educate ur students how it works, ur better off with a consumer product that scans for tags. those rfid tags might not work rly well if lets say the calc is in a bag

Sounds like you have to look for tags and detection gates as used in shops to prevent shop theft. Probably cheaper and more reliable than trying to roll your own (unless your time is free).

Preferably I would like to build a simple system as detection gates are fairly large and obtrusive. As you say, it would be a good opportunity to teach STEM. Are there any modules that could detect tags?

go to and search for RFID. most of the work is already done for you. but,, range is going to be a big problem for you.

Is there something better than RFID that exists? I get that it’s a short range device, just need to find something better.

Just look up how shops do this.
Two key techniques, one is based on RFID, the other on special (de)magnetisable tags. Both based passing between two antennas which then can detect the presence of the tag. In case of the magnetic tags it’s just recording presence of a tag, in case of RFID they can even tell which individual tag is passing through.

Get big ugly calculators that they don’t like .