My Pl, router and modem are on the UPS, but not the power bar digital 6D (PAB).
Sorry, but I´m not shure what happens with a PAB device or with a Powerbar 6D.
The answer above is only valid for the standard powerbar with 4 pugs.

If PAB/6D digital part part is powered by the powerbar, you will lost communication
If PAB part is bus powered, Communication is still possible and the power may be recognized (or not)

Just missing how too put an alarm for the high or low voltage.
Not shure if it´s possible by now (in any case: a wishful option).
Anyone from GHL or with that powerbar should answer this.