There are several factors to consider when trying to decide which bat detector to buy. Here we list some of the most important to help you choose the best detector for your purpose.

To find and identify bats in the field:
If you have never owned a bat detector before you should purchase a heterodyne detector. This type of detector is the best for identifying bats in the field. You hear the calls in real time and you can differentiate between different tonal qualities and repetition rates of bat calls. You can also obtain the 'peak' frequency of the call which will be decisive in making an identification. Heterodyne detectors are simple to operate requiring only the adjustment of a volume control and a frequency control. The frequency control is similar to the tuning control on a radio.

To record bat calls for playing back:
You can use a heterodyne detector with a tape output socket to make recordings for playback from conventional cassette tape recorder or minidisc.

To analyse the calls on a computer:
Consistent and accurate species identifications can be made using sound analysis software. To do this you need recordings made by a frequency division or time expansion detector, plus software.

The type and quality of the microphone determines in part how sensitive the bat detector is. Piezo microphones are most sensitive at mid frequencies (45kHz). Electret are best at lower frequencies (<30kHz) and capacitance are very good for detecting high frequency calls (>80kHz). This does not mean you cannot for example pick up high frequency calls with a piezo microphone. It simply means that the distance you can detect them will be less than if you have a capacitance microphone.

This is a measure of how many kHz either side of your tuned frequency you can hear calls on. For example: if the band width is 8kHz then you will hear calls 4kHz above and 4kHz below your tuned frequency.

All the detectors are tuneable within the range 20-120kHz. This range is appropriate to detecting all European species. Pettersson detectors tune down to 10kHz. This makes these models the most suitable for picking up lower frequency ultrasound such as produced by some grasshoppers and crickets.

If the controls are on the side of the detector rather than the top it is easier to operate with one hand. Similarly, the smaller detectors are easier to operate with one hand. Weight is also an issue, particularly if you are carrying a tape recorder, torch and other survey equipment.

An LCD display makes the determination of frequencies easier, but this is a more expensive feature. The frequency dials on the lower cost detectors have a small backlight to help read the dial.

Most detectors have a built in speaker though you will probably want to use headphones at least some of the time.

Most detectors have an audio output so you can plug in a digital recorder, minidisc, tape or DAT recorder to record the bat calls.