How does xm satellite deter nonsubscribers from listening to its transmissions?

XM Satellite Radio deters nonsubscribers from listening to its transmissions primarily through encryption and digital rights management (DRM) technologies. The signals are encoded, requiring a subscription to access the content. Additionally, the use of proprietary receivers ensures that only authorized subscribers can decode and listen to the broadcasts, further limiting access to non-paying users. This combination of technical measures effectively protects their service from unauthorized use.