[Q] How is it that service providers like AT&T detect if your boot loader is unlocked topic

I'm not even sure if they can detect if your boot loader is even unlocked without physically having the device, but I did read that they don't allow phones with unlocked bootloaders on their networks, so if this is the case how do they detect it, can you bypass this at all? Because if they need the physical thing I can just restore it whenever I need their help. Any help would be appreciated :)
I'm planning on rooting a y536a1 huawei, if that's any help. Happy holidays!