# proximity sensor 2 meters

#### wertamaki

Joined Apr 14, 2020
3
Hi, can anyone help me with ideas on building devices that produce an audible signal when come close to each other, say 2 meters or less. Both devices continue signalling until they are two or more meters apart. Think about a microphone moved close to a speaker - you hear an unpleasant screeching sound until you move them apart.
Device requirements:
Portable: yes
Unit price: cheaper is better, max 5$each. Size: smaller is better, max cigarette-box-size. Sensitivity: audible signal if distance between units is between 0 and around two meters. No signal if distance is more than that. Power: battery operated PS. I read some articles on the topic, including Bluetooth IPS - used in museums e.g. But that would probably cost$. For a non-tech like me, microphone-speaker setup seems appealing, but two-meter-range might be hard to achieve in a cheap and small device...

Any ideas?

Wertamaki

#### AlbertHall

Joined Jun 4, 2014
10,783
How accurate does the 2 metres need to be?
Will the devices be oriented to face each other or is the system required to work wherever they are pointed (e.g. if one was in your pocket)?

Joined Mar 10, 2018
4,057

#### wertamaki

Joined Apr 14, 2020
3
How accurate does the 2 metres need to be?
Will the devices be oriented to face each other or is the system required to work wherever they are pointed (e.g. if one was in your pocket)?
No need to face or point. It should be in your pocket and signal when someone with same device approaches you in any direction. It should work on it's own, without pressing a button, pointing, etc.
Precision: +/-50 cm.

#### wertamaki

Joined Apr 14, 2020
3
Thank you for your input, but that is not much relevant.

The item in the second link requires direct sight of view and works only in one direction.

Search continues...

#### AlbertHall

Joined Jun 4, 2014
10,783
Light and ultra sonic are ruled out, so that really only leaves radio and I don't know of any system which would come close to your requirements.