Yes, at least they are if you don't mind taking something apart. The metal plated ceramic disks used to make beeping sounds in may appliances can also be uses as sensors.
good day sir, is this little speakers you are saying can be use as a sensor if I am going to convert sound to electrical energy? I am searching on alternative components for my school project because piezoelectric film will cost me a lot money
using piezo from old speakers or old greeting cards would mean lesser efficiency when implemented on projects. I would like to ask if there's any available brand new piezoelectric elements in the philippines?