Heterodyne bat detectors?

Question:Can anyone recommend a good heterodyne bat detector for less than £100? If you can, please tell me the pros and cons and even warn me of ones to avoid. Thanks.

by the way - this is in home and garden as I wasnt able to select the science category for some reason !

Answers:
This site might help.

And became a nice site to read, I have a bat flies round my home, nice to watch, I did not know you could listen too.

Nice Question