Cofounder of Totemic here. Just to add detail, it should be corrected in the article now but we don't use sound. Just as you say, we believe one major advantage of our system is not requiring behavior change on the part of seniors when that can be really difficult even if they want to because of memory and other issues.

We'll likely use one device for small apartments and have to scale up to 2-3+ for larger houses much like Eero does.