How Do Stud Finders Work?

Modern electronic stud finders operate by measuring the capacitance difference in the wall to identify where a wall is denser. By measuring the electrostatic field of a wall and detect slight differences in the flow of electrons, stud finders detect the relative change in density and thereby studs showing the best place to drive that nail. Some of the devices use magnetic fields to detect nail heads in the studs or to scan for wires. 

Here at Tool Tally, we’re going to break down the best practices.

female hands demonstrating how stud finder works to locate studs behind sheetrock

Sure, you could hang your pictures just anywhere. But there is always the likelihood of having your pictures and mirrors come crashing down if they are only fastened to sheetrock. 

You can’t rely on sheetrock to hold heavy objects. Sheetrock is crushed limestone held together with cardboard. It is not designed to support any significant weight. 

Whether you are hanging a mirror or putting up shelves, you need to understand the basics of wall construction. Most houses are created from vertical, 2″ thick by 4″ wide boards. For the most secure mounting, you need to affix it to the 2″ side that your sheetrock wall is also attached to. 

So you are aiming for the center of a fairly small target. 

This becomes even more important when you need to hang electrical boxes or light fixtures. 

For decades, the only way to find a stud in the wall was to go on a detective mission. Folks would measure distances off of a corner, bang on the wall to listen for different acoustics and tap or drill tiny holes in the wall to verify the stud’s location before performing the installation.  

This method has always been cumbersome and relied more upon the carpenter’s skill. (You also needed a tub of spackle and a can of matched paint to fix all of the extra holes you created.) 

Folks began using strong, rare earth magnets to find metal studs and nail heads in the wall. By sliding a magnet along the wall, it is possible to feel the slight “tug” of resistance when a magnet slides across a metal stud. This method also works for locating metal nail heads in the wall. This method was slightly better than rapping on the wall and listening for changes, but it still required patience and a little bit of skill. 

Building on that, magnetic stud finders used a little compass needle that moved when the stud finder was dragged across a nail. This added a visual aid of a compass needle helped the process, further improving accuracy. Later devices incorporated electromagnetic metal detectors that were more sensitive and accurate.  

These magnetic stud detectors are still available to purchase, and they sometimes offer added accuracy when used with a modern stud finder on thick plaster walls. 

image of a man hanging trending octaganol shelving with a stud finder

In the late 1970s, Robert Frankin came up with the idea of a capacitor plate to detect the density of the wall.  He sold the idea (and rights to use his patent) to Zircon corporation, who produced the only stud detector of this type. In the ’90s when the patent ran out, other companies such as Dewalt, Bosch, and Franklin Sensors began offering similar — and sometimes better — stud finders. 

These sensors work by using an internal capacitor that detects dielectric currents. Dielectric currents are a fascinating phenomenon that occurs in insulating material (such as sheetrock). Instead of conducting the electricity, the electrons in sheetrock separate into positive and negative charges. Where there is a stud, this separation — the flow of electrons —  is different. 

A stud finder detects the difference between where there are wall cavities and where there are studs using the dielectric properties of the wall. 

Zircon still commands a large portion of the market as one of the most trusted and innovative names in the stud-finding industry. 

Most of these stud finders are accurate to about three-quarters of an inch of wall thickness. We’re seeing more “deep scan” models that can sometimes read deeper — generally up to 1,5 inches deep in ideal conditions, but some higher-end models boast a 4″ or better depth capability.

This is more than enough sensitivity to be able to read through most modern sheetrock walls. However, there are areas where the tool will struggle. Sometimes these tools struggle when working with older lath and plaster walls. Some lathe and plaster walls also offer the challenge or using metal mesh in the plaster which can create complex dielectric constants and render most stud detectors useless. 

Additionally, it is very difficult to sense studs through ceramic tile. Some of the deep scan sensors are able to detect nail heads through ceramic tile, brick and  even 4+ inches of cured concrete, but that is about the best you can hope for. 

young couple remodeling wires in wall of home after cutting to expose studs and wires


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Tips and Tricks For The Best Results When Locating Studs

Wall scanners also do not work through carpet or exterior siding. There are a few reasons for this, not the least of which are a thicker depth and air gaps between where the sensor is and where the stud is. 

Some of these models use multiple “detectors” across a wider field of sensing to help “triangulate” a stud’s exact position more accurately. 

Users should also be aware of false positives that these finders can create. Sometimes wires or piping can trigger the finder and create the appearance of a stud. 

The best answer to avoiding false positives is to first locate each edge of the stud that you are planning to use. It won’t be accurate, but a typical stud will be about 2 inches wide. Verifying that your stud finder is finding edges at approximately 2 inches apart, will give you some confidence. 

For increased confidence (and as a best practice) locate the stud on either side of the one you plan to drill into.  Most modern houses are built on 16-inch studs. By locating more than one stud, you can make sure that you are seeing a predictable pattern. 

Once you see the pattern of three or more studs, you’ll have that added assurance that you are actually getting ready to drill into a stud and not into a pipe or wire. There are scenarios where a stud may be off-center.  If you are unsure, mark the stud in a few places from floor to ceiling. If you are still unsure, drilling a small hole beside the stud and probing with a wire coat hanger (or even using a cheap scope) can help provide complete assurance. (this is typically only significant concern in a bathroom or kitchen). 

Multi-mode sensors are becoming more affordable and are a handy tool to have in every garage. They are excellent at detecting wood and metal studs, but they can also find pipes and live electrical wires that you will want to avoid (live AC detection).  An excellent example of this would be the Multiscanner x85 from Zircon. 

Future Technological Developments

Here in 2019, we are standing on the verge of yet another revolution of technology. Micropower impulse radar is creating the possibility of hand-held radar stud locators that will allow the contractor or homeowner to scan a wall and identify wood studs, wires, and pipes at depths much greater using radio waves than is possible with a stud finder. 

Currently, that technology is still significantly more costly than a standard stud finder. It is also still somewhat imprecise. For the home improvement contractor who does a lot of remodeling work, it can be worth the investment as it saves in labor to know what is going on behind the wall. But it will likely still be several years before the average homeowner can afford them.

Working blindly can be costly. And while it still takes a little bit of sleuthing to figure out what is going on in the space behind the wall, stud finders work with magnets, capacitance, and micropower impulse radar to make it easier. 

Just don’t run out of batteries.  

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