I live in Seattle and I've not had a visual alarm in either apartment I've lived in, nor do I recall seeing one in any I've visited, generally pre-90s construction. Not saying you're wrong, but the visual thing is far from universal and relying on owners accommodating disabilities can be a problem - my grandma can tell you about that. Ideally what you say would be all we'd need, but in the meantime I will certainly keep this app in mind!

Edit: I didn't meant to imply that I, myself, am deaf, only that the places I've lived didn't have visual alarms.