The problem with this method is that deriving a count from a recording is tedious and time consuming, but camcorders can be useful as a backup in roost emergence counts to observe bats re-entering the roost. Many Sony camcorders are sensitive to infrared. Infrared beam devices usually consist of a dual array of invisible IR beams. The size of the roost entrance determines the number of beams necessary and thus the power required and potential for off-mains use. Single beam DIY systems are available for bat boxes but these do not log the direction of transit. Almost all the systems in use today are non-commercial or DIY. A system in use in some mines in Wisconsin uses two arrays of beams however they are spaced quite far apart and consequently only log approximately 50% of the bats although extrapolated figures are achieved through correlation of time stamped video and beam break data. The Countryside Council for Wales (CCW) uses two similar systems with beams spaced close enough together that every bat transiting the entrance is logged along with the temperature. These systems require either mains power or 12 V deep cycle batteries. They can be used in conjunction with an Anabat Zcaim installed in a 6" soil pipe and pointed across the roost entrance to discriminate between species by correlating the time stamp data from the IR array and filtered Anabat Zcaim data for horseshoe bats (relatively easy due to their easily identifiable CF echolocation which can be filtered automatically using Anabat software). Data from beam break systems must be carefully analysed to eliminate "light sampling behaviour" (environment sampling) where the bats repeatedly leave the roost and return immediately if the conditions are not suitable. Some systems discriminate for bat-sized animals; they determine if the beams are broken by a bat sized animal and ignore all other transits. It is important that data is analysed using a methodology which takes light sampling behaviour into account. The method which seems to give the most accurate results is as follows: "out" transit assigned 1, "in" transit assigned -1. Start count is set to zero at 4 p.m. daily. Using a spreadsheet, the counts are added cumulatively from 4 p.m. each day until 9 a.m. the next day. The maximum "positive" count can easily be found for each day. Since every transit is time stamped, the exact time of the maximum daily count