If you only want something that is a siren, the Utilitech Siren (also sold under a couple other brands) is dated at this point but still works well. Even its quiet setting (there's a jumper inside the battery compartment to change it) is quite loud, and it sounds like a "real" siren--a complaint that I, like the above, had about others marketed that way (the Dome Siren is great for chimes when it responds fast enough but is a wimpy, tin-ny sounding siren). It takes 4 C batteries, and it's still going even though I don't think I changed them since I installed it more than four years ago. The new Aeon Doorbell/Siren 6 isn't bad, either (the Doorbell and Siren are the same except that the doorbell comes with a doorbell and doesn't cost much more). However, it does need to be USB powered. I would not recommend the older versions.