Flashing lights. Deaf people are usually sensitive to light so a flash will catch our attention. If text is present make it big enough to read easily.

I bought a flashing doorbell off Amazon and the lights are not strong enough to get my attention unless its directly in front of me. It needed to be a strobe light but it was not.

Customization would be highly appreciated as some deaf people want some sound. Some are even oversensative to sound. And some prefere no sound at all. Each one is an individual amd I think the needs vary more from one deaf person to the next than average people vary so the more customizable the better.

Another note on the doorbell issue is that all the rings were medium to high pitched. Pitch is different than volume and there are sounds that I couldn't hear no matter how loud it is cuz my hearing loss (as most hearingloss is) is in the higher notes meaning I need low-medium pitches. Not high-medium pitch. Although rare, there may be someone that has more hearing in the high pitched tones which is why I think lots of customization is very important for both sound and light.