Anyone at all curious about bats should get one of these! I wasn't sure if we had many in our garden but after going out tonight with one I found at least six in a half hour period, possibly more (difficult to tell if it was the same bats flying around).

The detector I purchased is a Magenta Bat4, it picks up the bat sonar brilliantly and is light enough to hold in your hand for long periods. Highly recommended by me, well worth the money! They cost around £55 - £65.