The easiest and least costly way would be to install a key box with a four digit cipher lock on or near an entry door that would be used by emergency services. These key boxes are made by a major manufacturer and are readily available at most "big box" stores and hardwares. The box location and code can be given to the 911 operator at the time of the call or placed in the 911 database. Check with the local jurisdictions 911 director or supervisor concerning the requirements for this. Some folks give a key to a trusted friend or neighbor, but that dosen't always work as that person may not be available to respond.
The other side of the story is that emergency services will do whatever it takes to gain access to you if you need help. That means forcing doors, breaking glass, etc.
As an emergency responder, I have on numerous ocassions, had to do physical damage to property to gain access. Whatever it takes.