user83049: So i am creating a haunt project that needs a way of detecting when an Arduino passes it and makes that Arduino do something. the problem I'm having is that none of the transmitter and receiver that has a small enough range that won't interfere with other patrons walking through on the other side of the wall. does anyone have any ideas what i can use?

user71575: There is a discussion of a similar question at the Arduino forum where they leaned towards passive UHF RFID tags.
If your budget stretches to it, there would be a range of active RFID tags that might suit.
There’s a good intro to RFID at Sparkfun, and Wikipedia has a good starting reference point.

83049: <p>So i am creating a haunt project that needs a way of detecting when an Arduino passes it and makes that Arduino do something. the problem I'm having is that none of the transmitter and receiver that has a small enough range that won't interfere with other patrons walking through on the other side of the wall. does anyone have any ideas what i can use?</p>
 71575: <p>There is a discussion of a similar question at the <a href="https://forum.arduino.cc/t/arduino-rfid-tag-detection/139570" rel="nofollow noreferrer">Arduino forum</a> where they leaned towards passive UHF RFID tags.</p>
<p>If your budget stretches to it, there would be a range of active RFID tags that might suit.</p>
<p>There’s a good <a href="https://learn.sparkfun.com/tutorials/rfid-basics/all" rel="nofollow noreferrer">intro to RFID</a> at Sparkfun, and <a href="https://en.wikipedia.org/wiki/Radio-frequency_identification" rel="nofollow noreferrer">Wikipedia</a> has a good starting reference point.</p>
