Novice looking for wireless advice

Hello forum, I am fairly new to making electronics. That being said, I could use some advice on my next project.

This device needs to be able to send and receive data from one unit to another. There will be several units involved in this project, but each unit should be able to identify a programmed pair. Say it’s several robots, two robots are mated pairs in a sea of hundreds of robots but they only interact with each other. When one comes within a 10ft range of its pair, it signals a switch to turn something on. What it’s supposed to turn on, I can’t say.

The overall size of the project needs to stay small; within 1inX5in. With that, I fully expect restrictions to the application. If anyone has some advice on what to use or where I should look for info, I’d be greatly appreciative. Also, if someone would like to help further into this project, please feel free to email me at bchainmail@gmail.com