Programmable siren (~DIY)
Sometimes there appears a need to build a siren with a special signal, for example, when building some special sports equipment, fire alarms, etc. Buying a special siren can cost more than $150 while its audio may not be satisfying, therefore buying an alarm siren may seem a good choice.
Unfortunately, it's not that simple. Sirens available on the market have some drawbacks. For example, piezoceramic oscillator siren has a small audibility distance due to its physical peculiarities: piezoceramic oscillator works well only on its resonance frequency which is usually above 1.5KHz, i.e. on high frequency that fades out fast in the atmosphere and also hardly skirts obstacles. Alarm distance of such a siren is not big, with usually automobile-like sound since its main application is car alarms.
There are dynamic oscillator sirens available on the market that can effectively work in a higher range of frequencies, have a good hearing distance, but they usually also are car alarms with a specific repertoire of sounds and melodies, so it's hard to find something more special.
In despair, manufactorers install what's available on the market, but it's not always rational. Here is a real case showing why a custom signal siren may be required. During a woman's basketball tournament, final siren sounds, built-in in the score-board. One of the teams stops playing while the other keeps running with a ball until the judge starts waving his hands. The latter team had an impression that it was a car alarm outside.