I built a little box,(including an LED), that screamed bloody murder when the power went out, until silenced. Then again when the power came back, until switched back to normal. My friend told me that he just happened to wake up early that morning during a power failure. He switched his mom over from an O2 concentrator to bottled O2. The thought of what might have happened to his mom scared the hell out of me. I was late for dinner because I was building the box to take over the same day. After his mom passed away, I gave the box to my stand-in dad, who had started using supplemental O2.
Joe