Alternative implementations for a door sensor - doorbell indicator

Product used: Xiaomi Mijia Smart Door & Window Sensor, but any door sensor will do

I wanted to know when some one rings my doorbell to notify me when I cannot hear the doorbell, when I am in the garden for example. In combination with a webcam I can see who is at the door when I am not at home. I know that there are products on the market that can fix this, most of them are not visual appealing, are expensive, and/or requires you to pay a monthly subscription. I think my doorbell looks fine, so I do not want to change this, and to be honest: it is more fun to make something yourself!
The model of doorbell I use works with two magnetic coils which actuates a metal rod which then hits the bell. Magnetic coils can also activate reed switches because they are magnetic, so let's try that! I taped a door sensor next to one of the two magnet coils to see if it will work. After some moving the sensor around and ringing the doorbell I found the best spot. I marked it and glued it to the bell. Done!

An extra step can be to be able to make it more visual appealing by moving the sensor to a better spot and extending the reed sensor. This is much the same as the lock reminder (see my other post about that), but instead of the battery spring you can use a separate reed switch. Be aware that the reed switches have a direction to activate so check that the plates are pointing to the coils.

For the automation, just make a script when doorbell switch closes then notify phone and start webcam recording. Due to the characteristics of the doorbell coil the sensor might register multiple open/close actions, you can filter this in the automation.

Alternative: vibration sensor, easier but less effective

I also tried by just placing a vibration sensor next to the bell, this also works but needs tweaking because you can get a lot of false positives by closing a door, walking around, and even a truck passing by my house or anything else that can cause vibration.