Monitor with transmitter battery back-up needed.

[NinePeedles]

Please can anyone recommend a good baby monitor that has battery backup in both the transmitter and reciever? Audio only would be fine.
I need something that will still work in a power cut.

Our cordless phone had a baby monitor mode we used when the kids were younger.

Calls would still come through on the downstairs handset only and you did have to remember to set it back on the right mode when you hung up but for us it worked well. It ran on the phone batteries but as most of the time they were on the base charging we were not constantly changing batteries.