20 minutes - but the bloody things just reset and start again.
The only answer is to cost the twits who can't control them some money - ring your local council and get their noise nuisance team out to break in and turn it off.
I've done it round here - funnily enough the serial, repeat offenders have become a lot more careful since the £250 bill ...
When my sister came back from holiday one year it was immediately obvious that their alarm had gone off whilst they were away.............not one of the neighbours had bothered reporting it.
Noise making alarms are anti-social and utterly useless - the police won't attend unless the home owner is inside the property and in immediate danger.
The only effective alarms are 'silent' ones with a fast-reponse service from a private security company - but that comes with a hefty price tag.