After another difficult night I hope someone here at SC can give me some advice. I have two basic questions.

1st question.

We live in a somewhat rural area that is subject to power outages. Our home has Firex model i4618 smoke detectors hard wired with battery back up. My problem is that whenever we get a power outage some of these units chirp? Even if they have a brand new battery installed they chirp when they lose AC power.
These units are not old, (some less than a year), and not all of them do this. Is the chirping some type of warning that the AC is off? Once they begin chirping, they will not stop until AC power returns, or you disconnect the battery from the detector.

2nd question.

My four year old golden retriever actually freaks out when he hears the chirping. I am not sure whether it hurts his ears but he actually seems to shake in fear.
Is this a common problem for dogs?

Finally, if anyone can direct me to a better brand of smoke detector or another solution to stop this chirping when the power goes out, please let me know.

I appreciate your input!