GMS120 Digital Multi-Scanner

I have much experience with wall scanners. As an avid handyman, I've tried them all, still searching for the golden one that actually will find wall studs with better than 50 percent accuracy. And by 50 percent, I mean 1 empty drilled hole for each one that is actually drilled into a stud.

What I liked about this sensor is that it has exceptional build quality. It feels like a precision instrument. The battery compartment actually has the contacts built into the compartment instead of having those awful fragile snap clips on the red and black wires trailing out of the instrument. The display backlight is exceptionally nice. I like that you don't have to keep a button pressed while scanning, just leave it on. If you forget to turn it off, it auto offs in 5 minutes. The metal scan mode is quite nice and the best working sensing feature of the unit. The instrument is nicely made and generally well thought-out. I like that it comes with a case. The wrist strap is very thoughtfully provided and something these scanners have needed for a long time. Bosch seems to have tried hard on this effort.

What I didn't like is the illuminated ring. It turns green, yellow, orange, and red but so what? It tells me nothing that I can't see on the display and it is too confusing/flashing to make any sense. You can get a particular color display and then scan back over that same spot and get nothing. You'll find, I think, that you'll ignore the light eventually and concentrate on the LCD screen which is actually reporting what is happening with the scan. The unit is nearly blind to AC wiring. Sometimes it hits, sometimes it misses. I would not bet my life on there being no live ac when this unit reports such.

Scanning an interior wall I constructed myself, and knowing where all the studs, firestops, wiring etc. are, I often could not find a clear indication of a stud. Tapping the wall still works best for me. I'm sending the Bosch back since, for me, it is no better at finding studs than I am by rapping the wall with my knuckles.

I live in an attached home with metal as well as wood wall studs and plumbing that runs through the attic and down the walls. Just about the perfect test bed for wall scanners.

The way this scanner works is a bit unintuitive. The user selects one of three modes; wood, metal or live electrical. When you select wood, the Bosch actually scans for all three. Selecting metal excludes wood, so you're scanning for metal and live electrical wire. Selecting live electrical limits the scanner to only that. Indicators in the display show what the scanner is reacting to; wood, metal or live electric.

The Bosch GMS120 did well scanning for wood. Since I live in an attached home, my neighbors and I are separated by a cement block fire wall. My dry wall is attached to that using thin furring bar. The Bosch reliably found the furring bar even against that dense slab of concrete.

When scanning metal, the Bosch attempts to determine if the metal is magnetic or not. That's useful to me, for instance, so I can tell if I'm detecting a steel wall stud or a copper water pipe. The Bosch gets it right most of the time, but not always. Sometimes magnetic metals are identified as non-magnetic. Still, the Bosch did a good job of finding metal studs. On interior walls, I could even identify studs supporting the wall I was scanning and studs supporting the other side of the wall. I could tell the difference by the signal strength displayed by the Bosch.

This wall scanner had the hardest time detecting live electrical wire. All the wiring in my home is simple 3 conductor plastic insulated wire with no shielding. Still, the Bosch could not detect most of it even when I made sure electricity was flowing. My guess is that the Bosch detected wiring best when it was lying against the underside of the drywall being scanned.

The Bosch is a useful tool and a good addition to your toolbox. Just remember it's a tool to help you find things in your walls, not the final word. So don't drill into your wall directly above a light switch just because your scanner didn't find electricity there! Use common sense, and you and the Bosch should get along fine.

Gosh, I'm on the fence with this unit, and disappointed in myself that I jumped the gun before the Amazon reviews were in. If you buy this unit, by all means purchase from Amazon or another reputable retailer with a good return policy in the event you are not satisfied with its performance. I'm reserving the right to upgrade this 3-star "It's OK" review at a later date, but for now (after a couple weeks of ownership), this is where I'm calling it.

I bought the GMS120 to replace a couple of older Zircon units that proved OK on drywall over fir framing, but I've moved to a more challenging climate of plaster walls, some with wire mesh.

But first, on drywall, the unit has been hit or miss. I broke it in on a wall that's open on the back side (so the framing is exposed), and I'm not getting the precision I've come to expect with the center-finding Zircon unit I own (which has also been hit-or-miss). Where the Zircon projected a finely focused LED beam along the calculated stud center, this Bosch unit gives a LCD "bar graph" display plus a 1/2" wide lighted circle that changes from red to yellow to green -- so the user is responsible for tracing a circle, or drawing a crosshair inside the circle, to note this location. The indicated center of the stud is often not repeatable, so it takes a number of back-and-forth scans to get a good feel for where I should be drilling. And on the drywall over metal stud walls at work -- big disappointment; no usable readings.

On plaster, I've been confounded by this unit's inability to locate a stud correctly. The instructions recommend placing paper or thin cardboard backing behind the sensor to assist with the uneven thickness / density of plaster walls, but the 1/4" lath appears to be too much to overcome. Never mind when chicken wire is in the mix. I'm going to keep playing with this and find a hopeful solution, as according to the reviews out of various European publications I've read, this shouldn't present an insurmountable challenge.

Worse yet, the current sensing function seems to be entirely non-functional. I've traced over known, energized wire locations with nary a *beep* from the scanner. Another reviewer states that this current sensing function is active in the wood scanning mode (I stated contrary previously and stand corrected), but I've yet to receive an accurate current warning from this scanner, regardless of mode selection). If I recall correctly, the Zircon stud finder sensed electrical current when in stud finding mode, so where two passes are required with the Bosch, the Zircon would somewhat reliably call out a live wire while in the process of scanning for studs. This function works if I place the sensor directly on live Romex or even a power cord plugged into a wall socket, but once drywall is sandwiched in the middle, readings disappear.

And the LCD display... what was Bosch thinking? There's a lot of info on the display, and it's backlit (user selectable on/off -- yay!!) but the viewing angle turns to zero if I hold the scanner just a FEW INCHES below eye level -- ZERO, as in INVISIBLE -- it appears the thing powered off. Higher than eye level, no problem, but lower -- even with the backlight on, it's completely unreadable. Seriously, Bosch? This may not sound like a big deal, but consider for a moment how you hold your arm while using one of these gizmos. I can't speak for the wider user base, but I feel most natural / comfortable with it at chest / neck height, exactly where the display goes blank.

The scanner comes with a rather thorough multi-language instruction manual, which shouldn't be necessary for something so simple. Nevertheless, it's true to Bosch's tradition and appreciated. It also comes with a tight fitting canvas-style case which truly could be just a tad bigger.

I'm holding out hope that I'm missing something important here and I'll grow to love this unit, based not only on Bosch's reputation, but on the stellar reviews I've read in various trade mags. Honestly, I'm not seeing this as being any better than the scanners available from Zircon, and the half-viewable LCD display is an absolute disappointment.

My last stud finder purchase was 6+ years ago, and after reading some great "pro" reviews about this unit, I was fully expecting that the state of the technology had greatly advanced versus the Zircon that was already in my tool bag -- especially coming from Bosch! I'm in the process of contacting Bosch customer service to see if perhaps I have a lemon, because again, my experience has been nothing like the reviews I've read proclaiming the GMS120 to be the best in class.

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