UHcom 2pcs DC 3-24V Active Piezo Buzzer with Lead Wire High Decibels Continuous Sounder Electronic Buzzer Alarm

they claim 3-24 volts abut 3.7 volts would not activate the buzzer

جيد والصوت غير مزعج

I installed these in parallel with the DC-powered electric door strikes on our building entrance doors. Converting the door-release system from AC power to DC silenced the "buzzing" sound the strikes previously made when AC power was applied, which made the unlocking nearly silent. These buzzers work perfectly to replace the unlocking "buzz" with an audible tone, which alerts visitors to the door being unlocked so they can enter. Despite being so tiny, these buzzers are loud enough that I ended up wrapping each one in a couple of layers of electrical tape to muffle the sound a bit, even though they're fully enclosed inside the door frame, tucked behind the electric strike.

I purchased these for a friend who had just gotten a Cahon (Cajon / sit-upon drum) and wanted to rig it for amplification. As many people know, piezoelectric transducers can act as microphones as well as tone emitters; they are especially effective at picking up percussive sounds. These are working well for that purpose.

Used these for a science experiment modeling how telegraphs worked with my kids. I'm thankful that it came in a two pack as the first buzzer did not work. I put in the second and it worked fine. The sound is quite high pitched, my kids even commented on the shrillness of it and how they wouldn't want to listen to it all day.