Gather all bits needed
Place them all on 2 mounting boards for your own convenience.
The 2 barograph readout are only for illuminating purposes.
You can omit these if you would like.
Powering and usage
Use a wall outlet adapter for long usage, or a usb power bit.
Pair your ble with your smartphone.
Adjust the 2 oscillators to a nice tuning sound. Set both switches to square.
Set the top timeout bit to off-on and the lower bit to on-off.
Adjust the 2 timeout bits to achieve a proper delay between the 2 sounds.
Adjust the filter cutoff to a warm sounding chime.
Make your relatives aware to use their smartphone when they are at your door :-)