It's the sound that will blare across Melbourne in times of trouble, but Tuesday was just a test run of the city's new public warning system.
There are 130 speakers at 65 locations, with more on the way, designed to broadcast an alarm and alert for emergencies, including a terror attack, riot, siege or hostage event.
"Hopefully, we never have to use it and we'll only ever use it as a test mechanism, but it does provide a really important additional tool for Victoria Police," Police Minister Lisa Neville told reporters.
"In the future, it has the opportunity for the City of Melbourne to use them (speakers) for things like White Night, New Year's Eve, to guide people with really important information."
Another 60 speakers at 30 locations across the city are due to be added by the end of 2018.
During the test, a siren blared before the audio message was delivered.
"Attention, attention, attention. This is a message from Victoria Police. This is a test of Melbourne's public address system. The sound you just heard is the standard emergency warning signal," the siren sounds.
Assistant Commissioner Stephen Leane told reporters the system would help police in a crisis and keep people safe.
"We needed to test this in case we had a critical incident or a crisis and we need to communicate to our community," he said.
"It's is a great opportunity to have a public address system."
The speakers are connected with the City of Melbourne's camera network.
Mr Leane wants community feedback on the test.
Sydney has had a public speaker system in place for several years.