Detect when 'transmitter things' are near (max 1.5m)

Hi guys.

Im quite newbie in electronic and Im trying to do a system able to detect when ‘things’ lets call it clients or transmitters are near (maybe from 30-40cm to 1m)

  1. I have to create the receiver or scanner and the transmitters, the idea is that one receiver/scanner have to be able to detect when this transmitter are near, around 30cm to 1m or 1.5m…

  2. These transmitter should be battery powered and have a long battery life, something like beacons bluetooths (1 year or 6 month?)

  3. when a person is carrying 2-3 transmitter and is walking in front of the scanner/receiver it should be able to read the three in max 1.5seconds… the time to walk in next to it.

Technology?

RFID: My investigation tell me that is the best, the transmitter in this case is a simple tag and is passive without battery BUT the cost of the antennas for the scanner is so expensive, I was looking that 1-2m RFID antennas is around 500-1000USD

BLE: With the popularity of BLE and beacons actually is a good idea, the beacons are every time cheaper and they have a good battery life, I can read the distance from the RSSI but the problem is how hard is found a BT module able to give you RSSI of beacons, MAC to identify the transmitters, and not like the HM-10 that only detect 6 max devices.

433Mhz: Im starting to search about it but im quite lost, I saw the tech is cheap, I guess I can identify the transmitter using a different transmision, the question is, I have to create wearable devices, then it should be thin and like i said, also with battery, how long can i setup a battery for a device that only is transmitting his identification code for not more than 1.5m?, Can i check the distance more or less in a efficient way (Without obstacle, in front of with clear vision, maybe only clothes)

the tile company has the perfect size and example of my idea.

What technology is the best? any new tech not described here?

Thanks.

This is a very difficult task that will require considerable expertise in low power embedded processing, radio frequency engineering and clever manufacturing skills.

It is not an Arduino hobby or learning project.

Reliable wireless is fairly easy. Reliable wireless that only works within 1.5m is very difficult.

I dont mind if is visible more than 1.5m, I dont mind if it exceed it.
(its only that its a lose of power/energy).

But then in the receiver, I should be able to filter thats signals that are near of 1.5 or less aprox. not very accurated. to see how is really near. (In front of the receiver)

Is that better? and possible?

I’ve been working with 433mhz stuff for several years and I’d say this isn’t possible. The RSSI measurements aren’t reliable enough, you’d probably get the same reading for 1m as 10 or 20 metres (if there’s nothing in between*).
BLE may be better, but still a difficult task.

*if you put your devices into a metal box, to attenuate the signals as much as possible, you might get somewhere.

Thanks for the answer Quilkin, Then is impossible to read the distance…

Can I reduce the voltage to reduce the signal to 1.5m aprox? or its not going to work if I go less 3.5v ?

See reply #2. I would add that having a sharp distance cutoff is impossible.

Understand... With BT I have the RSSI and the TX power calibration but its quite hard/impossible to find a BT module detecting Beacons, and the only one allowing it HM-10 have a 6 devices cap.