You are aware, are you not, of the OFF switches?
As notes earlier in the thread 2/3 can be turned off. Presidential alerts are mandatory.
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The broadcast alert system was not limited to "free over the air" TV and radio. Subscription TV providers (cable and satellite) are also required to participate in the Emergency Alert System. Those guidelines can be found in the Code of Federal Regulations, specifically at 47 C.F.R. § 11.11(a).
For cell providers, Congress made the program voluntary. The only reason you'll be "forced to accept" Presidential Alerts is because your cell provider voluntarily decided to participate in the alert program. 47 U.S.C. § 1201(a) ("The [FCC] shall . . . adopt relevant technical standards, protocols, procedures, and other technical requirements . . . to enable commercial mobile service alerting capability for commercial mobile service providers that voluntarily elect to transmit emergency alerts.").
I don't think show time or HBO has been interrupted. The major networks have but nick jr and the like don't.
Again I'm not against it being there, as much as I'm against the lack of the option.