Person to Person Pager

I am looking at developing a Personal Call System where we have :-

Patient has a wrist watch type transmitter
Carer has a pager in their pocket or on belt
Working distance of upto 1000 yards

Do you think there is a need and cost price market for this device or do people use the ones that cover 100 yards quite happily ?

My reason for developing this is my father and uncle both live with PD and it means mum can go into the garden or pop to a neighbour and still be called if there is a problem (ie. getting out of chair).

I like your idea.What is the furthest distance which could be in range