From Longman Dictionary of Contemporary Englishldoce_003_calarma‧larm1 /əˈlɑːm $ əˈlɑːrm/ ●●● S2 noun 1 [countable]DT a piece of equipment that makes a loud noise to warn you of danger I forgot to set the burglar alarm. Car alarms are always going off in the street. a sophisticated alarm system2 [uncountable]FRIGHTENED a feeling of fear or worry because something bad or dangerous might happenalarm at There is growing alarm at the increase in crime.in alarm She looked up in alarm. Scientists have said there is no cause for alarm.► see thesaurus at fear3 
TMC[countable] an alarm clock I’ve set the alarm for 7 o'clock. I was still asleep when the alarm went off.4 → raise/sound the alarm5 → alarm bells ring → false alarmCOLLOCATIONSADJECTIVES/NOUN + alarma burglar alarmNeighbours heard the burglar alarm and called the police.an intruder/a security alarmThe house has a system of security alarms.a fire/smoke alarmA fire alarm went off and the building had to be evacuated.a car alarm (=for when someone tries to steal a car)I was woken by a car alarm in the middle of the night.a baby alarm (=for when a baby wakes up and cries)Is the baby alarm switched on?a personal alarm (=that you carry with you in case you are attacked)If you are nervous, invest in a personal alarm.alarm + NOUNan alarm buttonHe hit the alarm button under the desk.an alarm systeman electronic burglar alarm systemverbsset off/trigger/activate the alarm (=make it start ringing)A window blew open, setting off the alarm.set the alarm (=make it ready to operate)Did you set the burglar alarm?an alarm goes off (also an alarm sounds formal)The thieves fled when an alarm went off.switch/turn off the alarmI entered the shop and switched off the alarm.
TMC[countable] an alarm clock I’ve set the alarm for 7 o'clock. I was still asleep when the alarm went off.4 → raise/sound the alarm5 → alarm bells ring → false alarmCOLLOCATIONSADJECTIVES/NOUN + alarma burglar alarmNeighbours heard the burglar alarm and called the police.an intruder/a security alarmThe house has a system of security alarms.a fire/smoke alarmA fire alarm went off and the building had to be evacuated.a car alarm (=for when someone tries to steal a car)I was woken by a car alarm in the middle of the night.a baby alarm (=for when a baby wakes up and cries)Is the baby alarm switched on?a personal alarm (=that you carry with you in case you are attacked)If you are nervous, invest in a personal alarm.alarm + NOUNan alarm buttonHe hit the alarm button under the desk.an alarm systeman electronic burglar alarm systemverbsset off/trigger/activate the alarm (=make it start ringing)A window blew open, setting off the alarm.set the alarm (=make it ready to operate)Did you set the burglar alarm?an alarm goes off (also an alarm sounds formal)The thieves fled when an alarm went off.switch/turn off the alarmI entered the shop and switched off the alarm. Examples from the Corpus
alarm• An alarm went off in his head as it occurred to him what a sitting target he was in his Baby.• Several oil-producing countries expressed alarm at the fall in prices.• It sounds like a fire alarm and enters my ears like a keening mosquito that I can not reach.• Some of the girls squealed in alarm.• Some of them had noticed the sea-fret by now and had jumped up in alarm.• She closed the door behind him, put her rape alarm back on the bedside table, and there they were.• The bank teller pushed the alarm button.• Fred Goodyear was so shocked that it was more than eight hours before he raised the alarm.• The Big Three began sounding the alarm in a big way when January sales figures were reported.alarm went off• An alarm went off in his head as it occurred to him what a sitting target he was in his Baby.• Not long after the lorry driver left, the water became more and more acid and alarms went off.• He slept badly for two hours and rose when the bedside alarm went off at three.• The fire alarm went off that evening - Tuesday, November 24.• About an hour before the the alarm went off.• The instant I breached the threshold, the alarm went off.• I had the window down, and when the alarm went off I could hear it clearly.• They caused about £800 worth of damage but fled empty handed when the alarm went off.alarmalarm2 ●●○ verb [transitive] WORRIEDto make someone feel worried or frightened I don’t want to alarm you, but I can’t find the key.→ See Verb tableExamples from the Corpus
alarm• This fish gives off a poisonous mucus from its mouth when alarmed.• It was also couched in language designed to satisfy or at least not to alarm a multitude of constituencies at home.• They came out of the last slopes of the Jebel without having alarmed anything more than a couple of herds of goats.• Many women are alarmed by suggestions of a link between the contraceptive pill and breast cancer.• Meredith shrank back, alarmed by the unpleasant intention behind his expression.• The damage to the marsh has alarmed environmentalists.• We don't wish to alarm people unnecessarily, but it would be wise to avoid drinking the tap water here.• Lieutenants Peel and Maloney succeeded in so alarming the men that they decided to march to join Paredes and the revolutionists.• However, a resurgence of working-class agitation during 1833-4 alarmed the Whig government and the propertied classes in general.Origin alarm1 (1500-1600) French alarme, from Old Italian all' arme “to the weapon” 