Do city bikes have trackers?

I'm curious to know, do city bikes, like the ones you see in bike-sharing programs around town, come equipped with trackers? I've always wondered how they're able to monitor the location of all those bikes and ensure they're available for use when needed. Is there some kind of technology embedded within the bikes that allows for real-time tracking, or is there another system in place to keep tabs on them? It seems like an important feature for maintaining the efficiency and accessibility of these bike-sharing programs.