Alarm clock shakers

[fervent meadow]

I thought about using the following with PWM out on a ESP32 or Arduino:
https://www.amazon.com/Dayton-Audio-TT25-8-Tactile-Transducer/dp/B009RGJ47S
https://www.amazon.com/Onyehn-Amplifier-Module-5V-12V-Arduino/dp/B07P38H4P8/

I'll keep you posted if I get my hands on an o-scope. I wouldn't be surprised if it was something like the above inside that alarm clock part.