I’ve started masking the base PCB of my WiFi doorbell and I am using both masking tape and Blutack. I discovered the Blutack while going through my stationery drawer looking for something similar to the latex masking fluid which is used in real electronic waterproofing. I had thought of using an eraser which would be soft and pressed onto the micro-USB port would mostly seal against the conformal spray. The Blutack is now my best friend for masking, even if the spray dissolves it some and leaves it sticky – but the easiest way to remove Blutack is using more Blutack, which worked very well on the PCB board.
Masked 
Blutack and wet conformal spray 
Dried conformal 
Finished board
I decided to leave the camera alone as it was already in a unit, and previous experience has taught me that getting near lenses with any type of fluid or compound invariably means that you leave smears, no matter how careful. As it is a single unit I’ll seal around its seating and hope that that helps prevent major water ingress into the rest of the mechanism. If the video feed fails, I’ll know better next time!
The speaker at the bottom is also hard to waterproof: cover it in conformal fluid or seal it in somehow would mean that it likely could not be heard, and similarly for the microphone which needs to vibrate to detect speaking. I’ll simply seal around the edges of those components and hope that their internals are okay with a little moisture.
The door-press button is difficult, as it needs to move to trigger the micro-switch, but isn’t sealed around its edge – I assume that rain against the front of the unit seeps through capillary action around the edges and into the major internal space, and thence via condensation onto other surfaces. That’s bad, as it possibly means I cannot seal one of the areas of major ingress.
Experimenting is fun, so I am going to try a thin film of plastic wrap (sometimes called ‘cling film’ here – other names elsewhere!) glued to the rear of the face plate to see if that works. The plastic film should bend enough to allow depressing the micro-switch, but the real challenge will be getting it sealed against the back of the face plate. I will try a rim of silicone sealant to which I will press a square of plastic film.
Untouched press 
Plastic film + silicone 
Trimmed 
Final – seems to be sealed
Overall the task took me the whole day. While that seems a little crazy (and you may prefer watching box sets on television), I saw it as a learning exercise and bit of a challenge! I’ve thought through how to waterproof a very difficult piece of equipment and although the proof that it’s successful still remains, I am overall pleased with the result and would attempt something similar with greater skill.
The doorbell does work now and I have tested it both via pressing the push button and the mobile app. Bring on the rain!
RandomAI 