I must admit I thought pagers used the gsm (cellular) network, but could only receive messages and therefore couldn’t be triangulated / located like a mobile phone.
https://en.m.wikipedia.org/wiki/Pager#Security
Reading deeper, if it’s radio signals then I can’t imagine Israel would have any problems replicating or spoofing them.
I’d imagine he’s could be worried about bumping into people in prison that he’s had a hand in putting there!
I can’t imagine judges are popular in prison, and corrupt judges are likely to be extra reviled.