ARD Nano, Mini/pro, Lilipad. They should all work.
can i use the GSM shield to notify the person in care through their handphones?
That I don't know, i've never had or worked with one before. Aren't the GSM shields kinda bulky, how do you plan on making the elderly use them? Are they going to be on them like a necklace / bracelet or mounted to their beds?