Getting Started

          In order to utilize this instrument to its full potential it is essential to read and understand these instructions.  First try the instrument in fair-weather before you use it during storms so you will have confidence in it when it is needed.  The M-10 is highly reliable and will tell you with certainty if any visible clouds have lightning.  It is designed to detect the unique signature of lightning – only lightning gives multiple bursts of 2 to several rapid pulses lasting about one second.  There are the "strokes" one sees at night as flickering within each "flash".  Operating it at night is quite useful when learning to use the M-10 so comparisons can be made between the detector's beeps and what you see with your eyes.

          The M-10 has been developed over a period of years and it will provide highly reliable information on lightning activity.  Because it detects light signals, it can tell if specific clouds it is pointing at contain lightning that can not be seen in daylight.  The instrument contains 2 independent sensing systems that can be operated separately or simultaneously.  In the directional OPTICAL mode (30 field of view) it will detect rapid changes in light intensity from lightning in a bright sunlit cloud (invisible in daylight) with sensitivity greater than the human eye at night.  In the non-directional electric field change (RF) mode, optimally used in the open away from overhead wires and structures, it surveys for lightning in all directions and has a maximum range of as much as 500 miles when held overhead.  The range is reduced to about 40 miles when placed on the ground with the lens pointing upward.

          Once you try the 3 different modes of operation you will soon see how the instrument works.  You will learn to identify the occasional false alarms that can occur in the OPTICAL or RF positions.  If you do not feel confident at first using these individual modes, it is recommended that you use the device outdoors in the combined (BOTH) mode where any beeps are almost certainly due to lightning.

          The best way to learn to operate the M-10 is by observing thunderstorms.  Nighttime lets you see how it detects visual flashes in the OPTICAL mode, but the distant invisible flashes picked up in the RF position are not observed optically.  For nearby clouds, the OPTICAL mode is the most unambiguous position and normally can be utilized.  Try the M-10 in non-thunderstorm conditions to identify possible sources of false signals in the different modes before using it during storms.  When you use it in non-storm conditions and observe that it does not go off when it shouldn't, you will have confidence in it during storm periods.

Field Change (RF) vs "Optical" Detection

          While "static" clicks from lightning on AM radios are well known, such signals are of little value since they could be coming from nearby or distant storms in any direction and are mixed in with much background "noise" from other sources.  It is instructive to compare the M-10 with a portable AM radio tuned between stations when storms are in the region.  Distinct beeps from lightning strokes are heard from the M-10 while background noise dominates the radio signals making it difficult to pick out the weaker lightning pulses.  OPTICAL signals tell you with certainty if visible clouds contain lightning.  The RF mode was added to the original purely optical design to eliminate false signals –- both an optical and electric field change signal (called RF) must occur simultaneously to trigger the instrument when in the BOTH mode.  Lightning produces both kinds of signals while sources of light and electromagnetic machinery produce only one type of signal.  Other advantages of the RF mode include: 1) the instrument surveys in all directions to complement the directional optical mode, 2) line-of-sight visibility is not required, e.g., lightning can be detected when operating in a deep valley with the clouds out of sight.  Generally the RF signals from more distant clouds come first, when dark clouds appear the OPTICAL detector will tell you if they contain lightning.

          Because most buildings have metal structure, which screens the RF field change signals,

This mode works best outdoors away from trees and buildings.  The M-10 can be used indoors in the OPTICAL mode by looking through windows at threatening clouds as the light signal goes through glass.  If you want to use the RF mode indoors for longer range (earlier warning) the detector will work with reduced sensitivity compared to outdoors in some wooden buildings; stand it upright on a windowsill.  Be aware that in buildings the RF section will be excited when dimming switches for lights are used and by electrical transients in wires caused by motors and turning light switches on or off.


          In order to test the OPTICAL mode, put the switch in this position (first detent from the "off" position"), point the detector toward a window (not at the sun) and flick your hand in front of the lens.  You should hear a beep every time your hand passes in front of the lens.  TV sets, video monitors and fluorescent lights are also useful for verifying that the detector is working.  Another optical mode test is to point the M-10 at a strobe light on an airplane, tower, road equipment, etc.  A beep should be heard for each flash – strobes go off about once a second.  It does not pick up rotating beacons as they do not change intensity rapidly enough.  It can be pointed accurately at a cloud or light source by sighting along the case.

          Next go to the RF position (second detent from "off").  By quickly touching the front gold colored plate (RF antenna) with your fingertip you should hear a beep.  (Sometimes you may have to wet your fingertip.)  Another test is to hold the detector in front of a TV set or video monitor and beeps should be heard.

          Finally, the BOTH position (third detent from "off" can be tested in the same manner in front of a TV or video monitor since they emit both optical and electric field change signals.

Battery Replacement

          If the detector does not beep when these tests are done, the 9 volt batteries may be low.  You should be alerted to low voltage because with the detector on it will beep every 3 seconds when the voltage drops below 6.5 volts.  The batteries can be replaced by removing the back plate which is held by two screws.  In removing and inserting batteries be careful not to damage the foam padding that cushions them; shake them out far enough so you can pull them out with your fingertips.  Use alkaline batteries rather than regular 9 volt batteries which do not last as long.  The end of the battery with the contacts goes into the holder first.  Note the contact orientation when the batteries are removed; the larger octagonal one is to the right when the switch is on the left side looking from the rear.  If the unit does not function properly with new batteries, verify that the battery contacts are being pushed against the instrument contacts, i.e., the batteries must be pushed forward slightly as the endplate is screwed down.  Use Radio Shack or Eveready alkaline batteries and not Mallory Duracell batteries which are slightly shorter and do not make good contact in the battery box.  Circular and hexagonal symbols on the bottom inner surface of the battery box show orientation and the rear endplate will not seat properly if one or both of the batteries is inserted incorrectly.  Alkaline batteries will last for more than 50 hours of continuous operation and considerably longer with intermittent use as in normal operation.  Be sure to shut the detector off when not in use to save the batteries.

General Information

          Distinctive sound pattern.   One of the patented features of the M-10 is the capability of separating individual pulses (strokes) present in most lightning flashes to provide an unmistakable signal.  (These can be seen at night as flickering pulses in the lightning channel.)  The sound produced is a distinctive sequence of several beeps lasting about ½ to 1 second, which is the duration of a lightning "flash".  Once you hear this sound pattern you will recognize it as caused by lightning and nothing else.  While most discharges have such multiple strokes, some have only one stroke and you will hear only one beep.   The multiple stroke pattern is detected most often in nearby lightning while single beeps are more frequent in distant storms when some of the weaker strokes are not detected.

          Environmental factors.   Like a camera or radar detector, the M-10 is not waterproof so if it is raining take it under a shelter or indoors and look through a window in the optical mode.  If it must be used in the rain, the two holes in the case (at the switch and tripod mounting hole in the bottom) can be easily sealed with tape.  Or the unit can be put in a plastic bag.  Within a car or building with raindrops splashing on the window, the OPTICAL section will be triggered by reflections from the drops.  To utilize it under these conditions use the BOTH mode with the detector close to the window pointing at the clouds.  While the M-10 will function properly in sunlight as long as the sun's rays do not strike the lens, it is a good idea to operate it in the shade if this is convenient.  The RF section is not sensitive to sunlight.  Keep the detector still when operating in the optical mode.

          Handheld or operated on a tripod.  You can hold the detector in your hand when pointing it at a cloud or region of the sky (OPTICAL or BOTH mode) or pointing upward to survey in all directions (RF/DISTANCE mode), but do not touch the gold colored brass plate (field change antenna) which will cause false beeps.  Since it is necessary to listen for beeps for at least 1 minute when lightning is not frequent, e.g., the beginning of a storm period, you will find it more convenient to prop the M-10 on something or use a camera tripod.  There is a standard size camera tripod mounting h ole near the center of the bottom of the unit.  Compact table top tripods can be used conveniently.

          RF provides an estimate of distance.  When you do not see thunderclouds, but want to check for lightning beyond the field of view, use the RF mode.  The detector is most sensitive if you hold it over head and the sensitivity decreases as you lower it to the ground.  Sensitivity can be judged by the change in beeping frequency, i.e., the number of beeps per minute.  With the detector overhead you can detect lightning 500 miles away, at chest height held away from the body, the range is about 100-200 miles.  If you put the detector on the ground pointing upward it is least sensitive so if the M-10 beeps the storm may be within 40 miles and soon at your location.  With the M-10 in the same position if the beep rat increases the storm is approaching, if the rate decreases the storm is going away.

          RF sensitivity is affected by the location of the detector.  The RF mode (electric field change) will lose most of its sensitivity when operated in or near a building, near a tree or any structure.  You should be at least as far away from the structure as twice its height.  Since proximity to metal structures reduces sensitivity, if you want to use the RF mode from a golf cart with a metal sunshade, get off the cart and step away from it.  Since the BOTH mode depends on sensing the OPTICAL and RF signals, the BOTH mode will not work well near a building or tree because there will be little RF signal.  To observe how the sensitivity is affected by proximity to structures, observe the beeping rate in an open area and then keeping the M-10 in the same position, e.g., out in front of you, walk toward a tree or building while observing how the rate decreases; there will be few if any beeps under a tree or next to a building.

          Calibration of distance with position.  You will learn from experience how distance to thunderstorms can be estimated from the position of the detector.  One way to do this is by comparing the height of the M-10 above the ground when RF signals can first be detected with storm location obtained from TV and radio broadcasts or by phone from the National Weather Service.

          The optical mode.   This section functions anywhere you have a view of the sky which can be from under a tree, indoors through a window (be sure there are no light reflections from the glass) and even under high voltage wires because the arcing and electronic noise will not be picked up by the optical section.  This mode is easiest to interpret – so when you see threatening looking clouds use the OPTICAL mode.

          When to evacuate?   Our general recommendation is when the lightning is 5 miles away which will allow about 20 minutes lead time.  Some users prefer 10 miles and lightning can come to earth from the thin cirrus clouds that blow off downwind from the tops of thunderclouds into regions with little or no apparent clouds well away from the convective storm center.  Often in the early or late stages of storms, when lightning is not too frequent, the distance to lightning can be obtained from the time between when the detector beeps and when the thunder from that lightning is first heard.  Sound travels 1 mile in 5 seconds, so divide the number of seconds from beep-to-thunder by 5 to determine the distance in miles.  If the time is getting smaller, the storm is approaching; if it is getting longer, the storm is going away.  The latter information can be used to determine when it is safe to resume activities.


          When people realize that they do not have to be hit directly by lightning to be killed or injured, they are more likely to take the threat seriously.  Also, it is not generally realized that when lightning is in an area all locations in that area are at risk.  The probability of the next ground strike is about the same anywhere within a few miles of the last strike, i.e., if lightning occurs within a few miles of a golf course the next flash is as likely to be anywhere on the course.  In most instances people affected by lightning are not hit directly.  Most of these occurrences are caused by transients, currents that flow trough people in the vicinity of lightning – people have been killed several hundred feet away from the place where the lightning came to earth.  These effects are caused by: 1) the strong induction electric field which exists in th e air near lightning, and 2) currents in the ground flowing outward from the ground contact point.  Any grounded object rising above the earth's surface (such as a person standing on a fairway or in a boat) will be subject to the induction effect which can cause a "streamer" of electric charge to flow from the earth up through the body and head into the air.  The second way is because of the potential difference between the feet (or parts of the body if lying down) caused by currents in the earth's surface.  This can cause thousands of volts to occur across the body; currents will thus flow up one leg through the body, and down the other leg.  The greater the distance between the feet the more the potential difference between the feet and larger the current flow.  The reason livestock are killed so frequently is because of the relatively large distance between their feet and the fact that they congregate under isolated trees for protection from rain.

          If you are caught in the open, these effects can be minimized by keeping your feet together and squatting down, but do not lie down.  Do not remain in an open area if you can help it; if there are dense woods nearby with trees of relatively uniform height get into the woods and stand midway between trees since lightning is less likely to strike such an area compared to isolated trees or hilltop areas.  Do not stand under an isolated tree or small group of trees because they will attract lightning.  You are better off staying hunkered down in the open.  Some shelters can be dangerous if they are up against an isolated tree since lightning can jump from a tree 3-4 feet to nearby people.  Do not hold up an umbrella or golf club which will act as a lightning rod and attract lightning.

          Do not remain in golf carts in the open as they will attract lightning and, unless completely enclosed by metal, will not afford protection.  You can stay in your golf cart if  you drive it into the above mentioned woods.  Stay away from open hilltops in favor of low ground and valleys.  Do not remove your golf shoes because you are afraid of being grounded by the spikes – you will be even more grounded with your shoes off.  Stand on dry cement if convenient since this will reduce the chances of being affected by ground currents.  Do not lean on metal fences which will attract lightning and conduct electric currents.  Do not use the telephone – induced currents can come into buildings and trailers along the phone lines.  The best thing to do is get into an electrically shielded structure such as a car or substantial building.  Many if not most, "golf shelters" on courses only keep the rain off and are unprotected from lightning.