Have used the same ol' zircon for over ten years. Dont know about their newer units because I haven't had to replace it. The one I have finds the edge of the stud, the newer ones locate the center for you. It's been reliable and dead on through the years. Here's a link to amazon.com:

Here is a link that might be useful: zircon stud finders

Are you sure about the way you're using it? For the zircon plus (or whatever it's actually called...xl, maybe?) from Home Depot, you lay it flat, push and hold the button in a non-stud area, and slide over until it beeps (which is the edge of the stud). You can double check by sliding toward the stud from the opposite direction to get the other edge.

Also, instead of a pencil, you can mark them with bits of blue tape - then you have no extra marks.

I say this only because I've seen folks point them toward the wall like a remote control or something.

kaiser-
I have yet to encounter an electronic stud finder that works consistently. I use the old-fashioned kind with a swiveling magnet to locate the screws or nails that hold the sheetrock to the studs. They're much cheaper, need no batteries, are quite accurate, and last forever.

Usually I locate 2-3 fasteners on a single stud and mark their positions on pieces of masking tape. Then I get a level to locate a vertical line between them if they are at all off from one another. One other trick is to use a 1/16" drill bit once you think you have located a stud: drill into the wall right above the baseboard to see if it is solid. You can smooth out the tiny hole with your fingernail, or use a tiny bit of spackling to hide the hole. No one will notice.

Sometimes if I want to be sure I'm right in the middle of the stud in order to put in a big fastener securely, I'll drill several small holes next to one another to find the edges of the stud.

Here is a link that might be useful: Stud finder

A small 'super magnet' is even better than the old magnetic stud finders.

Get about 5-6.
They will stay put on the fasteners in the drywall very well while you locate some additional fasteners, and then mark the spot.

They sometime will even work through plaster to find the nails holding wood lathe to the studs.

The Zircon works well on drywall, but has problems on plaster.

Some types of foil faced insulation will mess up a stud finder. I'll second the 1/16 drill stud finder. 100% reliable never misses.

Where can one buy a handful of super magnets locally? I'm assuming you're talking about the ones about the size of a hearing aid battery, right?

(I have one that latched onto the side of a pair of my pliers, but I can't remember when/where.)

"Where can one buy a handful of super magnets locally?"

I just order them on the web.

Get a decent number since they get lost and break if allowed to 'snap' together.

They sell them in the hardware department of my grocery store.

You don't want the watch battery size magnets. The thin disk magnets are plenty strong, but they have no range. They will work just fine if the nails are covered by a 1/32 coat of joint compound and a coat of paint, but if they are burried much deeper than that the disk magnets don't work very well.
I have some 1/2" dia by 1" long N45 magnets that work pretty well for most stud finding thru sheetrock.
I also have a couple of 1"dia X 1" long magnets that will find a nail burried a good 1/2" deep. Some care is needed in handling. They will knock the paint of appliances and draw blood if you get some skin between two of them.

The range of a magnet is proportioate to the Size.

"The range of a magnet is proportioate to the Size."

And what they are made from.

I have disks about 1/2 inch in diameter and 1/8 inch thick.

Thew will stick to nails under 3/4 inch of plaster.

My calculator shows .01 lbs pull for a grade N48 1/2 x 1/8 neodium magnet at 3/4" range. But that's measured in pull against a heavy steel plate. Pull is also proportional to the size of the object being attracted. Pull would be less against a sheetrock nail. your magnet is pretty light so yes i see it clinging to a nail under 3/4" but just barely.

It is much easier to take a bigger magnet and just wave it across the wall. I can feel the pull while it's moving.

sheetrock nails are rarely buried more than 1/4" deep.
at 1/4" range, N48 grade magnets:
.5 x .125= .25 lbs pull $.82
.5 x 1.0 = 1.19 lbs pull $5.25
1.0 x 1.0 = 10.61 lbs pull $13.

Pull against a sheetrock nail will be substantialy less than these numbers. In practice the 1/2 x 1 works pretty well. The 1" x1" works great. A bigger magnet would likely work even easier, but would be a real PITA to have around. I can pry the 1" x1" magnet off my tool box or wrenches or saw , etc. without too much dificulty. and it rarely draws blood when I get some skin under it. Anything bigger would be dangerous to just have laying around.

Even the little neodium magnets are hazardous to computers and pacemakers.

"Where can one buy a handful of super magnets locally?"

The attached link is to a manufacturer of magnets. Not sure if they require you to be a business - but we've purchased hundreds of magnets from them in bulk numerous times. I consider them a good, honest firm.

"Even the little neodymium magnets are hazardous to computers and pacemakers."

That is correct. Neodymium or 'rare earth' magnets are the strongest permanent magnet in the world.

They will pick up a US dollar bill because of the iron in the ink...

They can hold metal objects to one side of your hand, move metal on a board 2" thick... and two of them (if large enough) will go THRU your hand! (Hospital time.)

Their pulling power is enormous, and as with all magnets - is logrithmic to distance; and falls off substantially as air gap increases.

Neodymium magnets vary in 'quality'. They are sold/priced per density, saturation, and size.

So not all Neodymium are 'equal' in relation to a specific size or shape.

However - (even the smallest, least dense, and not much saturated) of them should not be viewed as a 'toy'; and should always be treated with respect in the handling thereof.

Not everyone NEEDS the most powerful Neodymium available - and it costs energy and $$ in electrical juice to magnetize - so the companies make them in various energy densities and saturations.

So it is impossible to say - this size Neodymium does this, and this size won't do that... Size and shape of the magnet affects how much total saturation and energy density the magnet can be given - not necessarily how much was actually put into it. :)

It is also interesting to note that Neodymium magnets do not have a magnetic knee curve.

Here is a link that might be useful: Magnet Source

dave-
Interesting points. Thanks.

And since you bring up the safety issue, I should mention that these are not toys to leave around small children. I read of a medical case a couple of months ago where a toddler had swallowed two of these magnets and as they worked their way through his intestines they got attracted to one another and pulled that section of the kid's intestine closed. He almost died from the bowel obstruction. Certainly a freak accident, but good to be aware of.

Here's a really cheap stud finder: Your knuckle + Your ears. With a little practice it works well. Often I will verify that there really is a stud that I found with my Zircon SF this way.

Lee Valley has a nice selection or rare earth magnets.

the studthud is supposed to be able to work on all construction. It's just being sold in Australia but should be in U.S. beginning of 2012

Here is a link that might be useful: studthud

"The studthud is supposed to be able to work on all construction."

Like every other solution it is going to have problems, especially with some of the older construction methods.

Like metal lath with plaster, or metal plaster 'forms' that so a lot of use for arches.

If the magnet is strong enough it will stick everywhere.

An to steel pipes in the wall for heating or water.

besides the fact that steel pipes aren't used for water and are not used for anything but steam heat, they'd be so far away from the studthud that they wouldn't effect the magnet.

"besides the fact that steel pipes aren't used for water and are not used for anything but steam heat, they'd be so far away from the studthud that they wouldn't effect the magnet."

Galvanized steel water pipes had a pretty long period of use after lead and before copper came into common use.

Threaded brass was also used for a while, but even then was painfully expensive (threaded copper saw a short period in the 1920s also).