Sounds like you have some APS model. I had those issues, and switched to Cyberpower. The alarm can be muted and the battery lasts for many years.
A UPS is a must for me. When I lived in the midwest, a lightening strike near me fried all my equipment, including the phones. I now live in Florida and summer outages and dips (brownouts) are frequent.
I've got Cyberpowers actually. The alarm can be muted, but it doesn't stay muted. Especially when the battery (or ups circuitry) is worn out so a power dip turns into infinite beeping. But also if the computer is turned off.
Many years ago I had the same thing happen - actually came in the phone line, fried my modem and everything connected to the motherboard. More recently I had lightning strike a security camera - took out everything connected to the same network switch, plus everything connected to the two network switches one hop away. Also lit up my office with a shower of sparks. Lightning is no joke.
A UPS is a must for me. When I lived in the midwest, a lightening strike near me fried all my equipment, including the phones. I now live in Florida and summer outages and dips (brownouts) are frequent.