DENVER — The calls to 911 raised an instant alarm: One caller said he shot his co-workers at a Colorado video game company and had hostages. Another in Florida said her father was drunk, wielding a machine gun and threatening their family.

A third caller on New York’s Long Island claimed to have killed his mother and threatened to shoot first responders.

In each case, SWAT teams dispatched to the scene found no violent criminals or wounded victims — only video game players sitting at their computers, the startled victims of a hoax known as “swatting.”

Authorities say the hoax that initially targeted celebrities has now become a way for players of combat-themed video games to retaliate against opponents while thousands of spectators watch. The perpetrators can watch their hijinks unfold minute by minute in a window that shows a live video image of other players.

“It’s like creating your own episode of ‘Cops,’” said Dr. John Grohol, a research psychologist who studies online behavior, referring to the long-running reality TV show that follows officers on patrol.

The players, who are often many miles away, look up their opponent’s addresses in phone directories, sometimes using services that can find unlisted numbers. They also exploit online programs that trick 911 dispatchers into believing an emergency call is coming from the victim’s phone or address. All the while, they conceal their own identities and locations.

Authorities spent an estimated $100,000 to send more than 60 officers in April to the hoax in Long Beach, New York. Investigators said the caller was upset over losing a game of Call of Duty when he called police using Skype. SWAT officers found only a teenager wearing headphones.

In Bradenton, Florida, at least 15 officers showed up at the home of a professional video game player on Aug. 31 after a caller posing as his young daughter phoned in a report that he was armed and drunk. Instead, they found him playing Minecraft for a live audience over Twitch.tv, an online network with millions of viewers.