It’s been a while since I’ve gone backpacking, but especially if I went solo I’d bring a locator beacon these days.
https://www.rei.com/learn/expert-advice/personal-locator-bea...
Sadly, if this person has been missing 30 days, probably the best bet of finding them is a cadaver dog - our SAR volunteers use them.
It's not as ideal as it does ultimately require a human to raise the alarm.
Also if something happens to incapacitate you for several hours out in the wilderness, you'll mostly likely be dead before help arrives--even with a beacon.
A locator that can be remotely activated (periodically wakes up to check for an activation signal) could be pretty useful, but I think it would mostly be used to locate bodies. Requiring solo hikers to carry something like that might be good alternative to parks requiring rescue insurance.