How to Find Metal Pipes & Wires Behind a Wall

Drilling one hole in the wrong spot can flood a room or shock you. Behind ordinary drywall run water pipes, electrical cables, and metal conduit — and you can't see any of them. Before you put a screw, anchor, or drill bit into a wall, take two minutes to check what's back there. Here's what's typically hidden, how to scan a spot before you drill, and how to check for free with the iPhone in your hand.

In this guide Why checking first matters What's usually behind the wall Scan a spot before you drill Check free with your iPhone Honest limits & safety Mistakes to avoid

Why you check before you drill

The two worst things you can hit are a water pipe and a live electrical wire. Nicking a copper or iron water line means a hidden leak inside the wall — often not obvious until the drywall stains or molds, turning a picture hook into a plumber's bill. Drilling into a live cable can trip your power at best and give you a serious, potentially fatal shock at worst. Both are entirely avoidable with a quick scan. The rule that saves people is simple: never drill blind, especially near outlets, switches, faucets, or a kitchen or bathroom wall.

What's usually running behind the wall

Utilities aren't random — they follow the framing. Knowing the patterns tells you where to be careful:

Electrical cable near outlets and switches. Wiring usually runs vertically up or down from a box, and often horizontally between outlets at outlet height. Treat the area directly above, below, and beside any outlet or switch as a hot zone.
Water and drain pipes near wet rooms. Supply lines and drains cluster in and around kitchens and bathrooms, and on the wall behind a sink, toilet, or shower.
Metal conduit and junction boxes. In many homes wiring is protected inside metal conduit or steel boxes, both of which a magnetic detector picks up clearly.
Screws, nails, and studs. The same fasteners that hold drywall to the wooden studs also register — useful, but they mean you have to tell a stud fastener apart from a pipe run.

Quick tip: Pipes and conduit show up as a long, continuous line — vertical or horizontal — while a single stud fastener reads as one short spot. If a signal keeps going as you sweep along it, treat it as a pipe or cable, not a stud, and drill somewhere else.

Scan a spot before you drill, step by step

Map the danger zones first

Before scanning, look at the wall. Note every outlet, switch, and faucet, and remember that cables commonly run straight up, down, or sideways from them. Plan your drill spot away from those paths whenever you can.

Scan the exact spot you plan to drill

Hold your detector flat to the wall and slide it slowly over the precise area — plus a hand's width in every direction. You're looking for any signal spike where you intend to put the bit.

Trace any signal to see what it is

If the meter rises, don't stop — sweep around it. Follow the reading up, down, and sideways. A long line that runs the height or width of the wall is a pipe or conduit. A single short peak is more likely a stud screw.

Move your hole, or cut power and water

The safest fix is to simply pick a clear spot a few inches away and rescan. If you can't, or you get a reading you can't explain, turn off the breaker for that room and shut the water supply before you drill, and go slow.

The free way: check with your iPhone

You don't need a dedicated wall scanner to do a sanity check. The Stud Finder – Metal Detector app uses your iPhone's built-in magnetometer to detect ferromagnetic metal — iron and steel pipes, metal conduit, junction boxes, screws and nails — and the magnetic field that surrounds a live electrical wire carrying current. It's the same sensor a hardware magnetic detector uses, already inside your phone.

Open the app and remove any thick case so the sensor sits close to the wall.
Hold the phone flat over your intended drill spot and tap start.
Slide slowly across and around it. Watch the live signal meter — a climb from green toward orange, with the alert, means metal or a live-wire field is near.
Trace the shape. Sweep to see if it's a long line (a pipe or cable to avoid) or a single point, then choose a clear spot to drill.

Scan before you drill — free

Check any spot for metal pipes and live wires in two minutes.

Download on the

App Store

Important — read this before you trust any reading. A phone detector finds ferromagnetic (iron and steel) metal and the magnetic field around live wires only. It will not reliably find non-ferrous copper water lines, plastic PEX or PVC pipes, or a dead cable with no current — none of those produce a signal it can read. A clean scan is not a guarantee that the spot is safe. Always treat it as one check among several: when there's any doubt, turn off the breaker and shut the water supply before drilling, and use a dedicated voltage tester for electrical work.

Honest limits and safety

Being clear about what the tool can't do is what keeps you safe. A magnetometer app is excellent at flagging steel pipe, conduit, junction boxes, and live wiring — and that already covers the most common hazards near outlets. But it is blind to plastic and non-current-carrying copper. If your home has PEX or PVC plumbing, or you're drilling into a spot where a pipe might be empty or a cable dead, the scan can read clear when danger is still there. For anything electrical, confirm with a proper non-contact voltage tester, and for plumbing, know where your wet rooms are and stay away from those walls. When you genuinely can't be sure, the answer is never to drill anyway — it's to understand the tool's accuracy, cut the power and water, and drill slowly.

Mistakes to avoid

Treating a clean scan as a green light. No signal means no ferrous metal or live-wire field was detected — not that a plastic or copper pipe isn't there.
Drilling right next to an outlet. Wiring almost always runs straight up, down, and sideways from boxes. Give outlets and switches a wide berth.
Skipping the breaker and shutoff when unsure. If you can't explain a reading, cutting power and water costs a minute and prevents a disaster.
Confusing a pipe with a stud. Trace every signal — a long continuous line is a pipe or cable, not a fastener. Learn to read the meter properly before you rely on it.