HiYou can make use of RFID

[GANEEV SINGH]

Hi

You can make use of RFID technology to do so…here's a link that might help you out to understand the process 

https://www.quora.com/In-Delhi-Metro-stations-there-is-a-big-yellow-thing-attached-between-the-rails-of-the-metro-track-at-constant-intervals-What-is-the-name-and-significance-of-this-thing