This electronic horn could have a better name (stop tittering at the back), but it's certainly pretty loud. At one yard it's apparently 105dB - not much less than the 115dB of the mighty AirZound. Pedestrians hear it easily, although the giant robot cicada noise can surprise them - it doesn't say 'cyclist coming' like a bell does.
Despite its 105dB, it doesn't seem to have a lot of 'punch' either: drivers can just about hear it from half a dozen yards, but only if the car radio is off and they're not in heavy traffic - so don't make any manoeuvre that depends on them hearing you. The horn is powered by a 9-volt 1604 battery (not included) and is held to your bike with a rubber strap. Its brick-like shape means that it fits securely underneath the bar, but this puts the front of the horn facing the floor - not ideal. The switch is strapped to the handlebar separately, on the end of a cable about a foot long, so it's easy to reach, even on drop bars.