Which Bat Detector?
A bat detector is a device used to detect the presence of bats by converting their echolocation ultrasound signals, as they are emitted by the bats, to audible frequencies, usually about 120 Hz to 15 kHz. There are other types of detectors which record bat calls so that they can be analysed afterward, but these are more commonly referred to by their particular.
Heterodyne Bat Detectors
These are the most commonly used and most self-build detectors are of this type. A heterodyne bat detector simply shifts all the ultrasound frequencies downward by a fixed amount so we can hear them. Look for a model with a digital display for accurate frequency readout like the Batbox IIID (approx£150) or the Magenta Bat5 (approx £95).
Frequency Division Bat Detectors
This type of detector detects all frequencies at the same time so there is no need to tune and you won’t risk missing any species. Recordings made using frequency division can be recorded for later analysis on computer.
The Batbox Duet (approx. £250) has both systems but only the heterodyne signal is fed to the speaker/headphones leaving the frequency division part for recording only. The Batbox Baton (approx £70) has just frequency division and produces sonograms as good as the Duet. It also comes with Batscan software. The popular Anabat system uses frequency division but is very expensive (£1400).
Time Expansion Bat Detectors
Time expansion detectors work by storing the call in their internal memory and then replaying it back 10 x slower thus lowering the frequency. The advantage of this system is that all frequency information is retained for later analysis. A major disadvantage is that when it is playing back a call it can’t listen for other bats. The other disadvantage is cost – typically over £1000.