1) Cockney rhyming slang for arm 2) One may be set for a vacation 3) Security device 4) Security measure 5) Warning signal of a sort 
(from the article `ultrasonics`) ...reflecting ultrasound off a flowing liquid leads to a Doppler shift that is calibrated to provide the flow rate of the liquid. This technique also ...
Physical security of a network requires that a computer room should be protected by a burglar alarm.
Burglar alarm is London Cockney rhyming slang for arm.
[n] - a loud warning signal produced by a burglar alarm 2. [n] - a warning device that is tripped off by the occurrence of a burglary
noun a warning device that is tripped off by the occurrence of a burglary
an automatic device for giving an alarm when a window, door, safe, etc., is opened or tampered with, as by a burglar.