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I swapped out the buzzer on my water alarm kit (All Electronics P/N MK-108) with this piezo siren. The result is a siren that can be heard very clearly two floors up. This unit has the ability to put out a louder, more irritating, sound than units twice it's size. The very low power consumption is the icing on the cake.
To the last poster: you cannot put a resistor in series to drop the voltage. Piezos have capacitance which is charged - which results in motion of the ceramic material - which is what you hear. Also, the chip which drives the piezo has a minimum operating voltage to function - which is not met with a resistor in series - due to huge voltage drops as the piezo charges.
To lower the volume, use a REGULATED supply of lower voltage, or if you use a series resistor - a cap across the module - consisting of at least 100 uF - paralleled by a 1 uF ceramic.
These approaches will allow you to get quite a dynamic range.
Our team used this for the recovery siren in our near-space balloon payload. (Along with a GPS Radio Tracker) We probably would never have found it up in a tree without it. Survived two flights so far, each more than 20 miles up in the atmosphere!
I had mounted this on my Harley to accompany the paging alarm, and it's a great item--just as earsplitting as advertised. My alarm modules were mounted forward of the rear wheel between the starter relay and the rear tire splash shield (dry side) up high.
The siren lasted well over two summers but eventually the elements got the better of it and now I need to replace it as the siren tone has become weak.
Know that it's a great buy, but if it's mounted out in the elements (weather), it will need to be replaced periodically depending on the ambient conditions demanded of it. It is NOT water-resistant or waterproofed.