They can track you with or without the IMEI. Next identifier is the IMSI read from your SIM card and I guess you're not replacing it every day...

Disclaimer: used to work in SIGINT, so please treat anything I say about this with appropriate skepticism.

There are people that for various reasons do cycle out their SIM card frequently as a means to avoid tracking. This is ineffective. Changing the IMEI/discarding devices entirely is more effective.

But if you change IMEI and use the same SIM card, you're still trackable as if nothing changed, right? The IMSI would be the same. I guess you need to change both at the same time...

Dudes have been driving around with fake base stations, rare, but has happened. Only sent spam sms messages with links but could be expanded with buying data from data brokers. A really serious crime though

I would think state level actors have enough tools to deal with this issue. If nothing else they could go the old fashioned way and just, you know, follow you.

It isn't usually the goal of SIGINT to only collect data about a target's location nor are targets always that easy to follow.