The best replacement for piezo is cavitron.

The best alternatives to piezo are rated as following:
★★★★★  cavitron
★★  magnetostrictive
★★  ultrasonic
★★  magnetic pickup
★★  magnetic buzzer
★  audio hijack
★  thermal inkjet
★  compression driver
★  transducer
★  soundhole pickup
  solenoid
  fsr

Your alternative for piezo is not listed? Suggest!
Speaking about piezo, one probably shouldn't forget about strobe.

Other search terms related to piezo and their ratings are:
★★★★★ strobe
You have in mind a companion for piezo and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of piezo in all years. Click on graph for more.
piezo
cavitron
magnetostrictive