In addition to what Peter D mentioned, if you're installing and/or servicing fire alarm equipment check with your insurance company and make sure you are properly covered to do this work. The premiums can be quite different from what an average electrician may pay. The main reason is that if the system fails and there is a loss of property and/or life, the lawyers use the "shot gun" approach to lawsuits. They sue anyone and everyone involved in the installation and maintenance of the fire alarm system. If you're not properly covered, you're on the hook - big time !!Just a word of caution about fire alarms. I have discovered that the codes for fire alarm systems vary drastically from state to state and even from city to city.