Hi! This is Nerd – a fan of useful tools for home DIY projects. This time I tested a shipment from China – model SH402, a four-line sensor with an LCD display that detects wooden beams, metal pipes, reinforcements and live voltage in the wall. Below is my review, rating and recommendations.
Technical features and functions
Detection modes: 5-in-1 system – detection read, metal pipes/rebars, voltage wires (AC), plus center edge locating in deep-modo for thicker walls.
Screen: Green LCD with backlight – displays mode, depth (e.g. ½”, 1”, 1.5”, metal up to 60 mm), and visual/beep alerts.
Power supply: one 9 V battery (6F22), not included; consumption is low - sufficient for several hours of operation.
Construction: PC/ABS plastic housing (~170 g), ergonomic grip, compact dimensions 17×7×3.5 cm. Available colors—most often silver or yellow.
Alarm functions: sound (buzzer) and LED warning when an object is detected. Automatic calibration supported.
My user experience
Preparation and start-up
Inserting a 9V battery, turning it on, selecting a mode – everything is quick and intuitive. Automatic calibration includes automatic reset when moving. The display is readable even in low light.
Beam and metal detection
On drywall, stud-mode quickly shows the edge and center of a stud up to a depth of 38 mm, while deep-mode shows up to 50 mm. Metal pipes and ribs are highlighted with a stronger indication.
Voltage detection
AC mode detects live wires right behind the wall, warning with a beep—the shift and the bottom of the wall pose no surprises.
Accuracy and stability
Edge and center modes work accurately if you maintain even contact with the wall. False readings can occur on drywall - you gradually learn how to steady the meter.
Advantages
Versatility: wood, metal, tension, edge/center and deep box—all in one tool.
LED display and audible warning: easier to distinguish.
Automatic calibration and easy to use: suitable for less experienced users.
Lightweight and ergonomic: you simply hold it and move it along the wall.
Low price, good for one-time or occasional use.
Disadvantages and limitations
Not professional robustness: plastic buttons, lightweight construction.
There is no certified exact standard: does not have laboratory-proven accuracy.
Sensitivity to gaps or filler in the wall – some internal structures may cause false positives.
Not connectable to the app – all settings via the meter itself.
Evaluation by criteria
| Category | Rating (★‑★5) | Comment |
|---|---|---|
| Functionality | ★★★★☆ | Useful 4-in-1 module for quick home use |
| Measurement accuracy | ★★★★☆ | It works, but sometimes with false detections in thin walls |
| User experience | ★★★★★ | Automatic calibration and display make operation easy |
| Housing and ergonomics | ★★★★☆ | Compact and lightweight, but the plastic doesn't give a premium feel |
| Price / value | ★★★★★ | Very affordable price considering the features |
Overall rating: 4.2 / 5 ⭐
Who do I recommend the SH402 to?
It is suitable for:
home users who want to quickly locate beams, metal pipes or wires before drilling,
lovers of DIY projects, partitions or hanging frames and shelves,
less demanding users who do not need professional precision.
Not best suited for:
professionals or craftsmen who need certified devices (e.g. Bosch DME),
working in very thick walls without depth confirmation,
wet walls or uneven surface without manual calibration before each measurement.
Conclusion
SH402 wall detector It is a convenient, easy and affordable tool for home projects.
Buy a metal detector from Nerd: SH402
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