Stud and cable detectors
A detector reduces risk. It does not remove it, and no honest page about drilling says otherwise. What these three tools do together is turn a guess into an informed decision — and give you a way to check the answer before the drill goes in.
Three tools, and a procedure worth more than any of them.
The Technoline states wood to 19 mm (0.75 in), metal to 30 mm (1.18 in), deep scan to 38 mm (1.50 in) and live cable to 50 mm (1.97 in) at 230 V. Four numbers rather than one, and the one that applies to a stud behind two layers of board is the 19 mm (0.75 in) — which is at or beyond the limit, and knowing that is what tells you when to stop trusting the tool.
The Bosch GMS 120-27 identifies the material and rings the marking hole with a three-color LED: yellow approaching, red on the object. Marking through the hole removes the offset between where the tool indicates and where the pencil goes, and a center indication finds the middle of a stud in one pass rather than three.
Before the drill, run a contactless detector along the line. It answers “there is probably voltage here”, never “this is safe” — but a pen that responds where the detector said nothing is a reason to stop and think.
Calibrate on the wall. Scan in both directions, twice. Mark the edges and the center. Look at where the sockets and switches are, and assume the cable runs vertically or horizontally from them. Then drill shallow first.
The commonest use, and one that a simple detector or careful tapping handles.
Where the stakes rise sharply. Live cable detection is the function that matters most and is the least reliable in awkward walls.
Metal detection finds copper; plastic pipes are effectively invisible to most detectors, which is a real limitation.
Where scanning a whole area rather than a single point is worth the extra minutes.
| What you want to avoid | Detector help | The gap |
|---|---|---|
| Studs and joists | Reliable | Little |
| Copper pipes | Usually found | Depth limits |
| Plastic pipes | Usually not found | A serious limitation |
| Live cables | Often found | Not if the circuit is off |
Detectors are simple electronics whose accuracy depends on the battery and on the sensing face being flat against the wall. A weak battery gives erratic results long before the device stops working, which is the failure mode that matters.
This is the guide where the safety section is the point of the whole exercise.
Wood 19 mm (0.75 in) · metal 30 mm (1.18 in) · deep 38 mm (1.50 in) · live cable 50 mm (1.97 in) at 230 V
The only detector here that publishes a depth for every material it claims: wood to 19 mm (0.75 in), metal to 30 mm (1.18 in), deep scan to 38 mm (1.50 in) and live cable to 50 mm (1.97 in) at 230 V.
Best for: Anyone who wants to know what the depth figure means before trusting it.
Metal, live cable and timber · three-color LED ring · center indication · IP54
A site-rated scanner that identifies which material it has found and rings the marking hole with a three-color LED — red on the object, yellow approaching, in an IP54 rubber housing.
Best for: Repeated drilling on site, where finding the center of the stud quickly matters more than reading a depth.
≈ $99
50–1000 V AC · CAT III 1000 V stated · LED, buzzer and vibration
A 50 to 1000 V pen stating CAT III 1000 V, alerting by LED, buzzer and vibration, and usable for tracing a break in a wire.
Best for: Tracing cables and identifying the live conductor in noisy or poorly lit conditions.
No. Damp plaster, foil-backed board, metal mesh and depth all change what the tool sees. Treat every reading as an indication, follow the manufacturer instructions, and assume a cable may be present where the wall makes one likely — above a socket, beside a switch, along a horizontal at ceiling height.
Because the physics differs. A scanner sees wood, metal and a live cable by three different mechanisms at three different depths, and a single headline figure on the box is always the deepest of them. One detector in this hub publishes all four.
It zeroes the detector against the construction in front of it. Wall build-ups vary enormously, and a detector not calibrated on this wall is reading against an assumption.
No. Plastic pipes are usually invisible to them, depth is limited, and live cable detection depends on the circuit being energized. It indicates, it does not guarantee.
Usually calibration: most zero themselves against the wall at switch-on. Starting over a stud or cable makes it invisible. A weak battery does the same.
Almost never when empty, and unreliably when full. This is the limitation that causes the most damage, and no setting solves it.
Commonly vertically and horizontally from sockets and switches. Knowing that is as valuable as any detector, though it is a convention rather than a certainty.
If you are drilling into a wall you cannot be confident about, isolating the circuit removes the most serious risk entirely.
Stop at once, do not withdraw a drill under power, isolate the supply, and get qualified help. Water and electricity both need proper repair.
Suited to: Anyone who wants to know what the depth figure means before trusting it.
Best figure: Publishes depth by material rather than one headline figure — the only detector here that does
Worst figure: Nineteen millimeters for wood is shallow — a stud behind two layers of board is at the limit
Suited to: Repeated drilling on site, where finding the center of the stud quickly matters more than reading a depth.
Best figure: Identifies the material rather than just signaling something present
Worst figure: No detection depths published in this listing, despite the model name implying 120 mm (4.72 in)
Suited to: Tracing cables and identifying the live conductor in noisy or poorly lit conditions.
Best figure: States CAT III 1000 V, the highest category on this page
Worst figure: Does not detect below 50 V, unlike the 12 V pens here
Targets, tripods and spares from the same aisle, at the price we noted. Check the thread matches the instrument you pick before ordering: it depends on the mount and the part number, which the listing states.
The instruments above come from the catalog of this site. Specifications are the ones the manufacturer states and the ones on the Amazon listing; prices are the Keepa reading for the date below, and both change. Ranking uses declared specifications, stated strengths weighed against stated limits, and price. Nothing here has had its accuracy checked by us, and the page says as much.
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Prices quoted in these summaries are dated readings. The live price is shown next to each product.
Thermal cameras, line lasers and clamp meters swing by thirty dollars or more across the year, and the biggest "discounts" often land at prices the same model sold for six weeks earlier. UniverTrack tracks the real price history across retailers, spots fake reductions, and alerts you when it is genuinely the moment to buy.
