USA and India.
There is no limit within reason (unlimited SOS alerts).
Please remember that if you send too many alerts, your "Alert Recipients"/"Emergency SOS Contacts" can simply opt-out of being your emergency contact, we will notify you if this happens and they will need to Opt-in from their phone.
We send them SMS's.
As many as you feel is reasonable to support you. it's up to you how large your network is.
You as long as their phone number is of these: USA. or India.
Anyone can be an SOS contact, you don't need a smartphone as long as the can receive a phone call, an SMS or an email they can be one of you emergency SOS contacts.