The office said to me, that service person would arrive 9 ish. The person called at 11:11. Am and said, he’d arrive in 20 minutes, he arrived &11:55. I was displeased about the late arrival. The service person apologize for being late, and explained and quickly removed the old co2 monitor & replaced and tested under 7 minutes. He went on to explain. How he didn’t know why the monitor didn’t signal it’s expiration, to the alarm center. but, that you need to check your co monitor yearly, well its replaced and done . Person apologize again for being late and very professional, approachable and works quickly. I’ve used SEI, since 1996,