If you have an old cell phone that is off contract (and who doesn’t?) and you can charge it, you can stage this phone for emergency use in a home-defense situation. Every cell phone, whether on contract or not, can call 911. You legally cannot have your ability to call emergency services cut off because you didn’t pay your phone bill.
The word perfect is a dangerous mischaracterization. Useful, possibly perfect no. Since the phone has no contract the 911 center has no way to ask a cell provider who owns the contract. This information is commonly used to give law enforcement a starting point when they lose a connection. As an example women’s shelters often provide these ‘free’ phones for 911 purposes but when they call 911 because their abuser has found them the 911 operator may not get their name in time and law enforcement has no idea who to look for. With a contract there will be a starting point
I am a professional in the area of cellular 911. Your comments are misleading. Many older cell phones were designed for cellular networks which no longer exist or exist in only very limited areas. These cannot make 911 calls. Examples of older networks are AMPS, TDMA and GSM. Most current networks are either UMTS or LTE. More details are available from the National Emergency Number Association (nena.org).