STUD FINDERS ($10–$50; $150)

ime was, anyone hanging a heavy mirror or anchoring a shelf hunted for framing studs by sounding across plaster with knuckle taps or probing with a parade of nails. By the early 1900s, simple tools holding magnets pointed to employ sensors to detect shifts in the dielectric constant of the wall—in effect, a change in density. , the most basic type, incorporate a single sensor that detects the stud edge as a change in density when the tool is moved along the wall. To work, edge finders first need to be calibrated to a stud-less section of wall, then they must be passed back and forth over the suspected stud to confirm position and center. , which are more sophisticated, employ two sensors that compare separate readings of the wall density to find a stud’s center. These tools also need to be calibrated, but generally they do their job in one pass. , the latest type, incorporate multiple sensors (as well as analyzing algorithms), so they take multiple readings from multiple parts of the wall. This yields more information, such as the presence of multiple studs and widths, giving quicker and more accurate results than other types. Also, instant finders do not need to be moved along the wall, reducing errors from bumpy surfaces or uneven plaster. The latest news in stud finders is . These tools emit small pulses of radio waves (often called micro impulse radar or MIR) that are reflected back by targets in a wall and detected by sensors. Though on the high end for cost, this technology is precise enough to distinguish a wide variety of materials—wood, plastic piping, electrical lines, rebar, even rodent movement—making it well-adapted to building rehabilitation and remodeling. Some products work in conjunction with a smartphone. Nonetheless, are not history. When the magnet finds metal, it darts to the spot with an unmistakable thud.