WHEN the United Arab Emirates announced last week that it would suspend BlackBerry service within its borders starting this fall, business travelers who rely on the handheld devices reacted with understandable dismay. But the decision was greeted quite differently by the men and women who make a living hunting terrorists, smugglers, human traffickers, foreign agents and the occasional team of clumsy assassins. Among law enforcement investigators and intelligence officers, the Emirates’ decision met with approval, admiration and perhaps even a touch of envy.

Why? Because just as professionals depend on mobile devices to do their jobs, law enforcement and intelligence officers depend on electronic surveillance to do theirs. The Emirates made their decision principally because Research in Motion, the Canadian company that provides BlackBerry services, refused to modify its information architecture in a way that would enable authorities to intercept the communications of select subscribers.

Monitoring electronic communications in real time and retrieving stored electronic data are the most important counterterrorism techniques available to governments today. Electronic surveillance is particularly vital in combating global terrorism, where the stakes are highest, but it is a part of virtually all investigations of serious transnational threats.

The ways in which individual governments perform electronic surveillance are highly idiosyncratic, controlled by a bewildering patchwork of laws and technical capabilities that vary from country to country, agency to agency, service provider to provider, application to application. Intercepting a land-line phone call, for example, is entirely different from intercepting a voice-over-Internet call, and retrieving an e-mail is different from retrieving a text message. For obvious reasons, governments (and former officials) do not openly explain how their electronic surveillance powers vary from one communications method to another.