Bats are hibernating from mid October to mid March or even later. Once warm evenings return and insect numbers increase bat activity increases greatly. From mid May to mid October almost every night will be suitable for detector surveys. Bats can feed even in heavy rain but severe cold and windy weather will greatly reduce the possibility of detecting bats.

Pipistrelle bats can emerge from their roost as early as a half hour before dusk. If you think you have a roost in your house don't leave it until after dark to look for the roost exit. Position yourself where you can see as much of the building as possible and keep an eye on the building rather than looking at the bat detector.

Noctule bats are a tree roosting species. They also emerge from their roost before is is truly dark. Most other species emerge in the 40 minutes after dusk and some such as Daubenton's bat can remain in the roost for up to 60 minutes after sunset.

Bat activity is at a peak between dusk and about midnight. There is less activity in the early hours of the morning but in the hour before dawn the activity will increase as the bats return to their roosts. Dawn is good time to find roosts as you can follow the bats back. If you are lucky enough to find a roost this way you may encounter one of the most interesting behavioural activities of bats, which is 'swarming'. As bats arrive back at the roost instead of going straight back in immediately they can swarm in large numbers around the roost entrance.

When bats leave the roost they usually disperse quite quickly to feeding areas and it is here where you will get the best results with your bat detector. Bats will go wherever there is a good insect supply so ponds, rivers and lakes are always good places to look as well as woodlands, hedgerows and wetland areas. Many urban areas still have some bats so don't think you have to be out in the country to find them. Parks, gardens, canals and areas of wasteland would be good starting points.

Learning to differentiate species using a bat detector is a skill which can take some time to learn. Some bats are simple to identify because the call is so distinctive or no other bat echolocates at that frequency. Others are harder to differentiate and other information about the bat such as wing shape or details of the habitat in which it is feeding may assist identification.

Wearing headphones will ensure you hear the weakest signals because background noise is reduced. Some bats, such as brown long-eared, have very weak echolocation calls and can be difficult to hear even at close range. Some detectors will allow you to hear the heterodyne call through one channel and the frequency division or time expanded call through the other.

Your detector is calibrated and tested by the manufacturer. If you build a detector from a kit then it should be calibrated. The simplest way of doing this is with a TV. Television sets produce pure ultrasound at specific frequencies. (Do not use computer monitors as there may be variations in ultrasound output). Turn the TV on and the sound off. Turn the detector on with the volume one quarter, stand at least 10 feet from the TV and point the detector towards the back of the TV. The frequencies produced by an analogue TV are at 31, 47, 62.5 and 78kHz. The frequency at 31kHz is the easiest to work with. Tune your detector to 25kHz and slowly rotate your control towards 35kHz. You will hear a pure note coming from the detector speaker which gets deeper in pitch as the frequency dial approaches 31kHz. At some point near the deepest note the detector will become silent. If at this point the dial reads 31kHz then your detector is properly tuned.

The standard 9V battery will power a detector left on continuously for 15-25 hours. Some detectors have a low battery indicator. If the display flickers or outputs become unstable, always consider battery replacement. A high quality alkaline battery is recommended.

Like any precision electrical instrument you should avoid getting your detector wet. In some circumstances you may want to use your detector in the rain. If so we suggest placing a plastic bag over the unit. This can be removed when necessary or you can make a small hole over the microphone access. If the microphone gets wet then there will likely be significant signal disruption and the detector will not work properly. The microphone will not normally be damaged but the detector should be placed in a dry environment to allow the microphone membrane to dry.