Sorry for forgetting that not everyone is healthy and young. Though I fear it's likely going to be an uphill battle for a little app like this to reach the people who aren't.

Young people can use this too. Just one example: at a "safe sex" seminar during freshman orientation, the organizer recommended letting your roommate or a friend know where you are going before meeting someone off of Grindr[0], etc. At the time I heard that, I actually thought of making something like this, though I never actually got around to it. I'm glad that someone has, though.

Another example: I haven't had to travel by plane since this summer, but my friends have told me to let them know the next time I have to go through security, so they can know that I made it through safely.

These are both somewhat niche use cases, sure, but the product is general enough that it can satisfy both (and, I suspect, many others). The concept of a "dead man's switch" is certainly not new or obscure.

As you can see, the application mimics behaviors that already exist in the real world. So, their challenge will not be finding real-life uses for this application, but rather marketing it in a way that people understand the variety of things that they can use it for.

[0] Grindr actually didn't exist then - it was probably Cragislist or something. Also, it wasn't really a "safe sex" seminar - Columbia calls their anti-sexual violence training their "Consent" campaign (colloquially referred to as "Consent is Sexy": http://health.columbia.edu/services/svprp/advocacy-outreach), but I digress.

So it's more an issue with the marketing choice of using taking a walk as the example, which I think is one of the worst possible options and possibly perpetuates a culture of fear.