There was once a 1960s BBC TV programme called 'Tomorrow's World' hosted by Raymond Baxter. On it was mooted, if not invented, a simple device (certainly by modern standards) which was attached to the WC toilet flushing mechanism.
This is the one mechanism in the house which is used several times a day. If the toilet was not flushed either for a settable period, or amount of uses, a warning light could show on the house-front.
For the elderly living alone this could be, I thought, a life-saver.
An elderly lady living alone in a large house across the road from me suffered a stroke or heart attack & lay for perhaps a couple of days or more, before someone thought something was amiss & called the police, but it was too late & she was dead.
This device could save valuable time to enter the house & give aid.
I know that there are now gadgets that can be worn round the neck, but how many people wear them & you may not be in a position or conscious enough to use them. This system would work automatically.