Channel 911

If an emergency such as terrorist biological attack happens, information about what to do and who to contact is transmitted on an otherwise redundant TV channel by the local transmitter.

Your TV is permanently looking for a signal from this channel (hopefully it will never find one), using the exact same technology as how car radios can look for traffic reports on all stations.

If a serious attack happens near a housing community, make sure they all know as fast as possible by switching all the TVs to the emergency channel automatically. People can flick back to the previous channel whenever they want however everyone watching TV gets to know of the attack.

Channel 911 would be government strictly controlled for emergencies only. This is different from 'government enforces all channels to show information about the attack' because people have the OPTION to watch their normal TV after they have their emergency information, rather than getting more scared and even panicky watching hours and hours of repeated police warnings. They know they've got to stay at home and they've done everything they can, now if they want to try and take their mind off the nightmare by watching 'Friends'. Let's let them.