Ryan Warner: Denver’s emergency alert system is getting a make-over. The sirens, which are scattered across the city, have been a regular presence for more than 25 years. The sound’s purpose is to alert residents to danger, primarily tornado warnings. Matthew Mueller is with the office of emergency management.

Matthew Mueller: Some look like a big bull horn, or bugle horn. Others are a rotating circular head. And some of them are on  top of a pole, and the older ones are mostly mounted on top of schools.

Reporter: Around 50 in all. Now, tornado warnings occur just a handful of times a year, yet people heard the sirens far more often than that. The reason? They were tested every month on the second Wednesday, at 11am. That monthly test is going away, as the city begins to update its system.

Mueller: So the benefit of the new system is that we can actually run silent test. So what that means is instead of actually ramping up and having the loud wail tone that everyone hears, it can run the parts, and unless you’re right there underneath the siren, you’re not going to hear it. But it does all the things that the test would do.

Reporter: The new system will also add more sirens. Now the alert will now reach new neighborhoods such as Stapleton, Lowry, and Green Valley Ranch. Workers expect to phase out the regular monthly tests and have all the new sirens up and running by the end of year. And for those nostalgic for the monthly tests - a small offering. The new sirens will be tested  aloud, once a year, probably in April.