Baby monitors in the test - What good are the parent soothers?

Baby monitors are supposed to monitor children's sleep. But in the test, only a few scored well in terms of range and endurance. Models with video often deliver poor pictures. It is worth comparing: some of the top models from the tests of the past years cost between 100 and 200 euros, but in the current test there is a good baby monitor that can be had for less than 40 euros.