I worked on a no-motion detector for firemen... it hangs on their jacket and if motion isn't detected for 45 seconds, it alarms... used for when a fireman is trapped, down, injured or unconscience. don't know what one would cost, or it it's available to civilians, but it might be worth looking at.
wow, that sounds great!!!

















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He is an older gentleman and mostly "trapped" in his house, so spends a lot of his time looking out the window and I happen to be in his vision. He usually makes sure that I do my chores safely and will call me if he thinks I need help.