Something to think about..
I saw another project (can't remember where now) where an object would either email or send you a text message when used. Imagine a coffee pot that sends you an email every morning. If placed in the elderly persons house, it signals that they are ok and have gotten up. No email or txt message signals a possible problem.
While I like this idea as the person does not have to wear a bulky device, the problem is deciding what does that person do every day to trigger a message. Other triggers might be opening the fridge door or flushing the toilet.