Overall score includes:

Audio/video monitors:
Picture performance (30%)
Sound performance (40%)
Ease of use (30%)

Audio-only products:
Sound performance (70%)
Ease of use (30%)

Performance assesses:
Sound range (how well it transmits through indoor walls).
Sensitivity and sound quality (whether the baby unit picks up soft sounds and how well the parent unit reproduces them).
Picture quality (of video monitors).

We also check for interference from a microwave or a digital cordless phone – and whether the monitor causes interference in a TV or a digital cordless phone.

Ease of use assesses:
The size and clarity of the labels, indicators and controls.
How easy it is to operate the controls and set up the unit.

Prices are from an August 2018 survey.