You do if your life depends on it. Also, if your family has put a cell phone on your bathrobe specifically for the purpose - even doing this is cheaper than buying special hardware just because it has mmWave.
> Nor will she be ok with me belting a phone onto her at all times.
But belting proprietary, un-auditable electronics to her or installing it in her private space is okay, right ..
The Fall Detector/home medical metrics industry is huge, and plenty of people are using cell-phone based Fall Detectors to protect their family. This doesn't require mmWave, one bit.