How can I find studs behind my 94-year-old plaster walls??

Prior to the 1950s, most walls were built using a combination of vertical studs, horizontal wooden beams called laths and plaster seams. Because standard stud finders detect a change in density inside the wall, they don't work on lath and plaster – the density inside these walls is not constant enough. If you have just moved into an older home and your stud finder isn't doing its job, invest in a metal scanner instead. Rather than sensing solidity, it locates the nails that fasten the laths to the studs.

1. Locate an electrical outlet on the wall. Typically, electrical outlets are attached to studs, so they mark a good place to begin scanning.
2. Calibrate the metal scanner according to the manufacturer's instructions. Slowly move it from left to right across the area above the outlet. Mark the spot on the wall where the scanner lights up,.Continue moving the scanner a few inches farther to the right, then reverse your direction and move it from right to left over the same strip of wall. Mark the first place the scanner lights up in the new direction. It should be close to but not on top of your previous mark. Split the difference between the two marks to find the center of the nail and therefore, most likely, the center of the stud.
3. Lower the sensitivity on the scanner slightly. Beginning at the nail, move the scanner straight up the wall. If it registers metal at intervals, it is finding a series of nails and you have found a stud. If it registers metal constantly, you have found a pipe inside the wall; in that case, sweep the scanner over a wider expanse of wall to find another spot where it registers metal. Repeat the process there.
4. Measure 16 inches horizontally from the first stud you find to locate the neighboring stud – most buildings are constructed with a stud every 16 inches. Scan that area to find nails and the exact location of the next stud.

A strong magnet will work. Find an outlet and remove the cover. Don't touch anything inside. Use a flashlight and see how it's attached. Usually they are screwed or nailed on the side to a stud. Then you can measure 16" from where it's attached to the next stud in the wall.

https://thecraftsmanblog.com/how-to-find-studs-in-a-plaster-wall/

https://www.youtube.com/watch?v=cYJ645mHXKs

https://www.instructables.com/4-Tricks-to-Find-Studs-in-a-Plaster-Wall/

You could switch methods and use command hooks or toggle bolts that don’t require studs. You probably have lathe behind it which is mostly wood but not very sturdy in many cases.

Use plaster anchors made of metal like a molly bolt or a toggle bolt. Be sure to use one that’s long enough to get behind the plaster and lath. When drilling into plaster, you’ll need to use a masonry bit.

Hello. Here’s a link they could offer some insight I hope this helps.

https://www.instructables.com/4-Tricks-to-Find-Studs-in-a-Plaster-Wall/

Hi Teri

Here is more info for you

https://www.youtube.com/watch?v=JOLRl8aqWFw

https://www.youtube.com/watch?v=cYJ645mHXKs

https://www.youtube.com/watch?v=rtEaQ_OcmRI

Stud finder

That's tricky and frustrating for sure. The above folks have good tips. Do note that studs are usually 16" on center, meaning from the center of one stud to the next, so if you find one edge, measure 1 1/2" and mark that spot for your stud thickness.