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An In-Depth Look: How Trail Camera Detection Circuits Work

An In-Depth Look: How Trail Camera Detection Circuits Work

What you need to know to maximize every camera in your arsenal.

Close your eyes for a few seconds and imagine this. You’re at your local big box retailer strolling through the trail camera section, you see numerous makes and models each with bright shiny packaging cluttered with impressive words… Ask yourself why?

As trail cam users, over the years we’ve grown accustomed to being sold products through repurposed made-up marketing terms like Multi-Zone detection or Reflex trigger technology….Their words, not ours. Instead of selling words on packaging to describe detection circuits, we would simply like the opportunity to help educate folks and explain the general concept. To truly understand how to get the most out of your trail cameras understanding its detection circuit is crucial and we’re here to help you do that, regardless of your brand of choice.

Let’s dive in by looking at what a trail camera’s detection circuit actually consists of and some of the technical lingo that goes along with it.

PIR Sensor

Arguably the cornerstone of any trail camera’s detection circuit, the Passive Infrared Sensor recognizes motion/heat by infrared radiation emitted or reflected by objects that will ultimately cause a trigger event….but how?

The sensor itself contains infrared radiation sensing element and is typically housed in a metallic case that is mounted to your camera's printed circuit board. The sensor elements are made of a material sensitive to infrared radiation and are placed behind optical filters or “windows” that allows the sensor to see a specified distance commonly known in the trail camera world as the detection distance. The amount of IR detected through each window by the element, which are balanced equally to one another, is considered to be the relative or ambient IR. When the sensor detects equal amounts of IR, the camera remains inactive. Trigger events occur when the sensor is able to detect a change in the relative IR from one element to another caused by motion and heat, also known as dynamic IR.

PIR sensors themselves are somewhat basic but become much more complicated when adding Fresnel lenses to complete the system. You’ve likely noticed the small black curved piece of plastic on your camera and in the past maybe even referred to it as the PIR sensor. While that is true, technically speaking the black plastic is actually a Fresnel lens array of the PIR system. On the backside of the curved plastic is an elaborate layout of Fresnel lenses. The responsibility of the Fresnel lens is twofold, to condense light providing a larger range of IR to the sensor and dividing the detection area into much broader more intricate zones than two large simple rectangular zones seen by the sensor’s “windows”. This is executed by the multi-facet sections of the plastic cover that have precision placed concentric ring designs known as Fresnel lenses. Each facet and sub-lens create and serve different detection areas while working collectively with the PIR sensor itself. The design and layout of the overall Fresnel lens are very important to the angle and overall zones of your cameras detection ability. 

While this is one of the more complicated and technical aspects of your trail camera’s detection circuit, once the overall concept is understood it truly makes a world of difference when thinking about efficient trail camera placement, while also grasping why false triggers occur.

Take Away

  • PIR sensors operate by detecting a change in infrared radiation
  • Fresnel lens design completes the detection zones and/or detection areas
  • PIR sensors work best detecting right angle movements


Detection Angle and Distance

As straightforward as it sounds, this specification refers to the angle and distance at which your camera’s PIR can actively recognize motion and heat/IR radiation to record a trigger event. As previously mentioned detection angle can be greatly affected by the Fresnel lens design while overall distance is subject to the PIR sensor sensitivity and circuitry.

While angle and distance alone are not necessarily that important, they each become critical when matched with camera’s FOV and trigger speed. For example, a camera with a lightning-fast trigger speed may have a detection angle narrower than the FOV, the faster the trigger speed the greater the offset should become. This type of design allows the subject to be in the frame before capturing an image. On the other end of the spectrum, a camera with a slow trigger speed may have a design where the detection angle is matching the FOV or slightly wider to compensate for the said trigger speed.

Take Away

  • Detection distance is dependent on the overall circuitry and sensitivity of the PIR sensor
  • Detection angle is greatly affected by the Fresnel lens design
  • Detection angle becomes critical when working with the camera’s trigger speed


Field of View

FOV, or field of view, is specifically referring to camera’s lens, this specification matters to users as the angle of what the camera can actually see. As mentioned above, the FOV becomes significant when matched with the camera’s detection angle and trigger speed.


The graphic above gives a good visual of how the FOV and horizontal detection distance changes in relation to the perpendicular distance from the camera. You can very easily see that the horizontal distance across the frame becomes exponentially shorter as you get closer to the camera, making the actual detection zone much smaller. The wider the FOV, the greater those horizontal distances become and vice versa.

While some camera manufacturers may specify their FOV under the camera's specs, many do not. When running cameras with a built-in viewer knowing the FOV becomes less important as users can see what the camera is capturing during the setup process. If the camera does not have a built-in viewer, understanding the FOV angle and horizontal distances come in handy to help save time not to mention multiple trial and error setups.

If you are interested in learning how to calculate your camera’s FOV please shoot us an email and we’ll get you squared away!

Take Away

  • FOV is the specification of what the camera is able to take a photo or video of
  • FOV becomes critical when matched with the camera’s detection angle and trigger speed
  • FOV is critical for users to know to help maximize every trail camera setup


Trigger Speed

From a consumer’s point of view, trigger speed is one of the most talked about specifications and rightfully so as it’s also the most marketed. Since the early years of trail cameras, we’ve seen major advancements on this front. On a technical level, there is a great deal that goes into obtaining trigger speeds, both in hardware and software applications, enough that for the purpose of this article we’ll explain from the 30,000 feet view.

Trigger speed of your trail camera is simply the amount of time lapsed from a trigger event (when the PIR detection becomes active) until the camera captures a photo/video. Many cameras on the market will have different trigger speeds for photo and video modes, often time’s video mode being slower.

The key here is to not only understand how the trigger speed works within the overall detection circuit but also know what type of trigger speed will work best for your applications. For folks running trail cameras on feeders and/or bait sites, there’s not much of a need for a lightning fast trigger speed, whereas someone setting up a camera on a trail during the rut may.

Take Away

  • Trigger speeds will affect how the camera is placed during setup
  • Trigger speeds determine what types of setup locations the camera will perform best at
  • Will affect how the camera is programmed to operate i.e. burst count, trigger delay, etc
  • Affects the overall design of the detection system


Recovery Time

The amount of time the camera can write/save data and then reset and be ready to take another photo/video. Again, many cameras will have different recovery times for photo and video modes, with video mode being longer.

Recovery time relies heavily on the hardware and circuitry design of the camera. Ultimately the speed of the processor will have the biggest impact. The faster the camera can collect and write the data to the SD card the faster the recovery time can be while maximizing the efficiency of the process is done through firmware.

On one hand recovery time can be one of the most overlooked trail camera specifications but one the other it can carry too much weight also. The availability of features such as burst count and trigger delay can prove to be critical and should be taken into consideration with recovery time specifications.

Take away

  • Slow recovery times can be countered by running burst modes
  • Fast recovery times ensure you more data to use as scouting intel by being available to take more photos

These 5 aspects working hand in hand ultimately make up your cameras detection circuit. While some cameras may flourish in one area but lag in another one might assume the detection circuit is only as strong or good as its weakest link. That is simply not the case. From a design and engineering standpoint, one specification can support or compensate for another. This is why understanding each aspect of a camera’s detection circuit and also the circuit in its entirety is paramount for maximizing your camera’s potential during every soak.