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Do these devices reset automatically after being triggered? If so how long is the interruption they make?
</quote>

The ones at Cecil Sharp House have to be manually reset. If one blows three times in a night then a circuit breaker trips which can only be reset after a time delay.

One band thought it a great joke to deliberately blow it twice in their first set. They didn't think it was so funny when they were told that they wouldn't get paid if they did it again.