An alarm was a device that gives an audible, visual or other forms of signal to inform people about a problem or condition.
Andro and Fabian were working in their repair shop when an alarm sounded as the First Doctor stole a TARDIS from the repair shop. (TV: The Name of the Doctor)
Alarms sounded on Platform One when metal spiders belonging to the Lady Cassandra sabotaged the station's forcefields, leaving everyone onboard unprotected from the deadly heat of the expanding Sun. (TV: The End of the World)
On Henry van Statten's underground base in 2012, Bywater set off the alarm and declared a Condition Red when the Dalek imprisoned inside the Vault broke free from its cell. (TV: Dalek)
An alarm went off on Floor 500 of Satellite Five when Cathica Santini Khadeni disengaged the safety on the Infospike broadcasting chamber to access the station's mainframe. (TV: The Long Game)
During the Battle of the Game Station in 200,100, alarms onboard the station sounded when the Daleks first forced the airlock on Floor 494. (TV: The Parting of the Ways)
The alarms of UNIT's base inside the Tower of London alerted everyone to the sonic wave created by the Sycorax ship as it entered Earth's atmosphere. (TV: The Christmas Invasion)
After using Rose Tyler's body to overpower the Tenth Doctor inside the New New York Hospital's intensive care unit on New Earth, the Lady Cassandra ripped a bunch of wiring from the wall and set off an alarm in order to summon the Sisters of Plenitude. (TV: New Earth)