When I was first involved with bats, there weren't many models of bat detectors available. The Bat Box III was king. A couple of types of time expansion detector were available for those with deep pockets and the low-cost option was the basic Magenta II heterodyne.
The Magenta was also available as a kit, but required some soldering skills. Luckily I'm a dab hand with a soldering iron, so it was my first bat detector, and it did a good job for me, whilst I learned some basic skills.
Today of course there are a plethora of types of detector on the market and the advances in technology over the past couple of decades have been simply amazing. I like to monitor what bat detectors appear for sale on eBay, mostly out of interest and partly in case any stolen ones turn up - I've lost a couple over the years. One machine that keeps appearing is the Haynes bat detector kit. At about £25 this seems and looks thoroughly cheap and nasty, so I've had no experience of it. However, I got to thinking about public bat walks...
To be honest, I'm no enthusiast for doing bat walks - there are much better people than me for talking enthusiastically about bats to groups of the public (TV is fine - they camera looks much friendlier to my mind). But occasionally there's nobody else and we shouldn't squander chances to influence people about bat conservation!
To give everyone an enjoyable experience you can never have too many bat detectors, but there are two problems: an armful of bat detectors costs a lot of cash. This isn't a problem for me, as I have access to the armoury of a well-equipped bat consultancy, but I'm not keen on handing valuable kit to random people who may, or may not look after it.
So I wondered if I could do something useful with one of these Haynes kits at minimal cost and so £25, including postage saw one landing through my letterbox. It's a very basic heterodyne bat detector and electronically very similar to the old-school Magenta II I first learned on, giving me a pleasant sense of 'coming home'.
It's a very simple kit - a well-made printed circuit board, with plug-in battery connector, microphone and speaker, plus knobs for the two controls It all goes together into the supplied case in about ten minutes (longer perhaps, if you read the instructions properly). And it works perfectly well as a simple heterodyne detector, ideal for bat-walks or kids.
The microphone is one of the old security ones, which has a pronounced peak in sensitivity around 40kHz. It works ok for Pipistrelles or Myotis bats, but is a bit deaf at the lower frequencies and the chances of picking up a horseshoe bat are probably negligible. But this will never be a serious piece of survey equipment, so why worry? Will they hear bats and be happy? Yes, they will.
It has draw-backs though. First, the case is cardboard. It's coated in some sort of polythene film, but robust, it is not. Secondly, the microphone protrudes from the top, in a manner almost designed to ensure it gets broken off. So, low-cost it may be, but it won't last long. Or will it?
A quick ferret about on Amazon secured me a solid plastic case for £12 (possibly a trawl through the local pound shop might produce a suitable bit of tupperware for less than that). I drilled a hole in the top for the microphone and two in the front for the two control knobs. Finally, a group of small holes allow the speaker to be heard. The nuts on the control shafts hold the circuit board in place and some heavy-duty, double-sided sticky pads hold the battery, speaker and microphone securely in position. I mounted the speaker inside, so that it peers through the hole in the case, thus protecting it. This probably narrows the field in which it picks up bats a little, but it seems ok.
To finish off, I dusted off the label printer from the back of my desk drawer and there we have it. For thirty-seven quid and less than an hour's light work I have a nice, solid bat detector, which should see many year's service, helping people to hear their first bats. It can probably withstand being dropped regularly and smeared in whatever sticky confection junior is munching. And if it gets lost or dropped in a river, at that cost I won't cry about it.
Given that nearest alternatives cost two or three times as much, I reckon it's worth making a few of them for your local bat group.
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