"Operative, this is Station Analysis. We have determined that a terrorist situation is occurring in your vicinity. As the nearest Squad available you have been assigned a Red BPN to deal with the terrorist situation. This BPN, reference #RED022924453-SA supersedes BPN #WHI022944563-DI that you are currently working on for the duration of the terrorist situation. Each member of the squad will be paid 200 credits and you are to proceed to the corner of Fifth and Wesson immediately. SHIVERS on the scene will brief you. This message has been recorded and by listening to it you are deemed to have fully accepted BPN #RED022924453-SA. Station Analysis out."
And the really annoying thing (besides the fact you can't just say no...) is that it always happens right in the middle of a surveillance, and you end up losing the person, or missing the vital clue that would have save you days of investigation work.
Oh well, such is life in the World of Progress...
Details of the emergency and its precise location will decide which of the above methods are used. For example, if there's a huge terrorist incident at the Spaceport, all three methods may be used simultaneously, as the number of squads required may be 'as many as we can get'.