Two things you cannot see in a wall without a special device — electrical cables and pipes. A detector is one of those tools that costs relatively little but can save you from a serious accident or an expensive repair. Here’s how to use it properly.
Types of Detectors: What’s the Difference
Three main types are on the market:
- Cable / wire detector: locates live and dead cables via electromagnetic field or induction.
- Metal detector — finds metal pipes, rebar, anchors, and screws inside walls.
- Moisture meter: measures the moisture content of a material by resistance (pin method) or electromagnetic wave (pinless method).
Most mid-range consumer devices combine two or three of these functions. Professional models (Bosch D-tect, Leica) cost more but are significantly more accurate, that’s what experienced handymen bring to the job.
Using a Wire Detector: Step by Step
Safety note: even with a detector, exercise caution when drilling. The device shows approximate location: not millimetre precision.
- Step 1. Hold the detector flat against the wall. Don’t press too hard: it can distort the reading.
- Step 2. Move slowly in horizontal passes, scanning from floor to ceiling in 20–30 cm bands.
- Step 3. When the device signals (beep, LED, vibration) — mark the boundary points on both sides with a pencil. The centre between marks is the centre of the obstacle.
- Step 4. Repeat the scan vertically (top to bottom) and compare results.
- Step 5. Only after two scans, mark a safe drilling point, at least 5 cm from the signal centre.
Using a Moisture Meter
- Pin method (contact): two probes are pushed into the material. Immediate reading, leaves small marks. Best for timber and plaster.
- Pinless method (induction) — held against the surface, no damage to the material. Less precise, but excellent for quick screening of large areas.
Reference moisture levels for timber: dry below 15%, acceptable 15–20%, wet above 20%. For concrete and plaster the scales differ: check the manual for your specific device.
Common Mistakes When Using a Detector
- Scanning in one direction only, a cable can run diagonally.
- Dismissing a signal in a partition wall: in older Warsaw buildings, pipes are often routed through partition walls.
- Trusting a single reading — always scan at least twice.
- Drilling immediately after a signal: mark, compare, find the safe spot first.
When a Detector Is Not Enough
Consumer-grade detectors have limited penetration depth: typically 3–5 cm. In thick reinforced-concrete walls common in older Warsaw blocks, readings can be unreliable. If you have doubts before a larger drilling job, order a professional survey — professional scanners show a cross-section of the wall without damaging it. Describe the job in the app, and a handyman will check the wall on site and give you the exact amount.
Rather not drill for the TV yourself? How a handyman fits a TV bracket is covered in the article on TV bracket installation. Just describe the job in the app and wait for offers from handymen.