A "loud alarm" refers to a very loud sound or noise made by a device or system to alert and warn people about a certain situation or danger. Full definition
She is curious about everything and has an extra loud alarm bark. (gsgsrescue.org)
If speaking doesn't do enough, you can even set off a rather loud alarm to deter people. (pocket-lint.com)
There are other types of «pick - up» lines out there however, which, while they may come across as sincere and hopeful, should cause VERY loud alarm bells to go off. (mirror.co.uk)