When out in the woods, I always keep an improvised whistle with me - and Dad and I used them to signal all the time (I said did because Dad has gone on his last hunting trip 2 season ago - his dementia and back are now bad enough he can't even leave bed)

Anyway - the improvised whistle? An empty .308 shell casing (well Dad's was a .300 Savage casing) - blow across the top of the empty shell, and it's not a great whistle, but it works

Just a thought for an emergency