Standard Floor

Does anyone have an idea on how to build a device to help me locate where to drill holes from my crawlspace?
I’m rewiring my house and I could just measure off distances to determine this information but thought it might be slick to build something that would help me determine where my wall outlets are in the room above me while I am in the crawlspace. My initial idea was to put a large magnet on the floor in front of the outlet and then go down into the crawlspace with another large magnet and see if I can get the two to match up. Then that would give me a good idea of where my drill point would be. Is there anything I can build that would do this electronically and is the magnet idea a viable one given a standard floor is probably only 2 inches thick or so of plywood between the joists?
The magnet idea seems like it should work although you might have more success with a cheap magnetic compass in the crawl space. You could then use a smaller magnet in the room.
You could just cut the holes for the outlets and drill down with either a long straight drill bit or with one of the flexible ones that you can get at large home centers or electrical supply stores.
Tagged as:
standard floor height,
standard floor joist size,
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standard floor length curtains,
standard floor loading,
standard floor plans,
standard floor register sizes,
standard floor thickness,
standard floor tile size,
standard floor tom sizes