So, the idea is to provide haptic feedback for the user when an alert is triggered, and when the alert has been received by a trusted friend. I found these very small vibrating motor discs which could be used to deliver the feedback (size 10mm diameter, 2.7mm thickness; 11000 RPM at 5V, 0.9 grams). These could just be switched on/off. Or else, we could use a small motor driver - e.g. the DRV2605 from TI - chip. This has an in-built library of various motor effects! You can see these waveform library effects in the datasheet here https://cdn-shop.adafruit.com/datasheets/DRV2605.pdf . So that would be pretty cool, in order to provide different types of haptic feedback for each situation! Adafruit already put the chip on a board (size 18mm x 17mm x 2mm, 1 gram) schematic here .