How Camera Traps Work

At the most basic level, it’s useful to know that camera traps need two things to trigger: movement and a change in ambient heat.

That means your camera will only snap a picture or start recording when it has recognised that something is moving past the camera and the camera has detected something warmer in front of it.

1. Something is moving past the camera.
2. The camera has detected something is warmer in front of it.

Clever sensors recognise that these conditions have been met and it can be really handy to know a little bit about them as well as some of the cameras other features to use it optimally. Here we'll run you through the foundations of how trail cameras work.

PIR Sensors & Detection Zones

Camera traps have a passive infrared sensor, or PIR, which looks for this combination of movement and change in ambient temperature. The PIR sends out strings, or beams, using what’s called the Fresnel lens. This is the curved bit of plastic that you can see on the outside of the camera that angles and points the beams to different areas. The area this covers is called the detection zone, or arc, and it can be really useful to keep in mind when placing your camera, as it can give you a great idea of how well your camera is positioned and what you’re likely to get in frame.

Of course, the sensitivity of each camera trap make and model will differ slightly as will the beams focus, but typically they form an arch from the bottom corner of the frame and rise up to the middle of the frame as demonstrated below. That also means the top of the frame on most camera traps is ignored by the PIR sensor - and makes good placement important for good results.

How to Make Detection Zones Work For You

Different animals will have different heat and movement signatures when moving in front of the camera - for example, a red deer is going to be far easier to spot than a woodmouse! That means that if you’re after large animals such as deer and badgers, you will see much greater detection distances than if you were after mice.

To give you some guidance we would suggest that if you are after smaller mammals and birds, you would need to put the camera closer to the target area - usually within 3 - 20ft (for small birds we would recommend placing your camera 5 - 10ft away). For something like hedgehogs, we generally recommend being within 5-15ft. The detection distances given on the product pages in the run down of the specs are generally based on an animal a similar size to roe deer or a human, for reference. You don’t really want a camera trap that would trigger for a mouse if that mouse is 80ft away, as you’d never see it!

Can Other Motion Like Grass Trigger Cameras?

A common question we get is ‘will a moving branch trigger my camera’? In essence, due to the above, it will not - a branch is not going to be a change in the ambient temperature, so doesn’t satisfy the PIR’s criteria. The same goes for moving water, grass etc. A good way to visualise this is to imagine a fox walking across in front of the camera. The fox is warmer than the ambient air temperature and moving - so the camera triggers. The fox then lies down in front of the camera and goes to sleep. The fox is still warmer than ambient air temperature, but is no longer moving. The camera therefore does not trigger, as both elements are not satisfied. The fox then wakes up, gets up and moves off. The camera trap would then trigger again.

However; the PIR can be fooled too. For example, if you’re somewhere like a forest and it’s a windy and sunny day and the sunlight is dappling on the forest floor and the wind is causing vegetation to move around - this could trigger the camera. The same goes if you have vegetation very very close to the camera’s PIR sensor - within 3-4ft. If this moves around, there may be a temperature difference between in front of the vegetation and behind it, so tricks the PIR into triggering. This is one of the big things that the major trail camera manufacturers put their research into; the quality and reliability of their PIR sensor circuit. Cheap cameras have poor detection circuits. Generally speaking, the more expensive a camera is, the better its detection and PIR sensor circuit will be.

Trigger Speed

A really important feature of all camera traps - this is how long a camera trap takes from the point of detection until it takes a picture or video. The PIR detects a change in ambient heat plus motion, and then wakes up the camera trap to start recording. Trigger speeds can be misleading though; photo trigger speeds are generally faster than video; there is more data in a video file, so it takes a fraction longer. Cheaper cameras will only tell you their photo trigger speed, as the video trigger speed will be very slow - usually more than 3 seconds. That usually means you just see the tail of something leaving the frame. At NatureSpy, we test both the photo and video trigger speeds. Most modern camera traps will trigger in around 0.5 seconds or less for videos, and photos will be similar or much faster.

Recovery Speed

This is how long a camera trap takes after finishing one photo or video until it is ready to take another. Generally, photo recovery speeds are much faster than video recovery speeds. Good cameras can be ready to take another photo instantly, with only gaps of 0.2-0.4 seconds between photos. Video recovery speeds are a little slower; the best camera traps can recover in 0.5-0.8 seconds. Poor quality and cheaper camera traps will have much slower recovery speeds. Recovery speeds are given in the NatureSpy reviews.

LEDs

This is how the camera traps can see at night - the infrared LEDs. These emit a light that is invisible to humans and wildlife. The cameras have a special filter which allows this light through - meaning you can get pictures and videos of wildlife at night without any disturbance. All trail cameras also have a small light sensor so they can determine when to use the LEDs and when to stay in color (daytime) mode. There are two main types of LEDs - low-glow (better for wildlife) and no-glow (better for security).

The Takeaways

1. A camera trap will trigger when something is moving past it and it has detected something is warmer in front of it.
2. It's the PIR sensor which recognises these 2 criteria are being met and sends out beams in an 'arc' which is the detection zone - basically the area your camera is looking at.
3. Read reviews carefully to see just exactly how fast your cameras trigger and recovery speeds are.
4. LEDs are how your camera sees in the dark; go for no-glow if using it for security.

Happy Camera Trapping!

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