Sensors that can detect gunshots have been installed in one of Britain's biggest cities in a bid to drive down gun crime.
The Shotspotter Gunshot Location System - which can pick up blasts within a 25m (82ft) radius - is being used in parts of Birmingham.
Police hope it will drive down the number of firearm incidents in the city, which have run into the hundreds in recent years.
The sensors, which record an audio clip and give police a GPS location, have been placed on buildings in areas of north-west Birmingham.
Trained officers listen in to the clips and can then decide whether to deploy other officers.
Chief Supt Chris McKeogh said the Shotspotter - used in 50 American cities - had an 85% accuracy rate.
He told the BBC: "The sound waves a bullet produces has a particular signature, if you like, and that should be recognisable to our force control room officers that have been trained up to listen.
"Shots, or a shot, being fired outside have the best chance (of being detected). Inside or with a silencer, the ability is not so good."
Birmingham has seen 295 firearm incidents, 59 involving discharge, so far this year. Last year, there were a total of 440, with 60 involving shots.
West Midlands Police said the rates of gun crime justified the use of the Shotspotter system.