Measuring unknown speaker/piezo element
Piezo elements measure as purely capacitive. If you connect them directly to an Arduino DIO pin then I'd put 100 Ohm resistor in series (to protect the DIO pin).

You cannot damage the piezo element with an Arduino output. If you set up a square wave of 1-2 kHz you may be able to hear them as a basic test, though some require 10s of volts peak to peak to use them at higher volumes.

Here is a common Piezo speaker that works at 5V p-p to give you some hints on what to expect.


Rated Current – 1 mA (Max)       
SPL @ 4 kHz/10 cm – 80 db    
Resonant Frequency – 4000 Hz (+/‐ 500)   
Capacitance @ 120 Hz – 13000 pF (+/‐ 30%)   
Operating Temperature – ‐20 to +70 °C