Look up the December 1998 Nuts and Volts magazine (Vol 19 No 12)
On page18 there is a circuit that shows how to make such a tester.  Yes it
uses the large amount of electrostatic fields that are present on an AC
line.
You can E-mail me for a scanned-in image of the circuit.
Craig

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Vincent Deno
Sent: Sunday, April 18, 1999 6:22 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [OT] EM Field Sensing


I'm currently working on a school project.  We're suppost to design a
simple system (simple to use rather) to detect a burnt-out bulb in a
Christmas light strand.

First idea which came to mind was sensing the EM Field produced by the
strand when a bulb is missing.  Could anyone better suited in EM fields
offer any advice?  A hall-effect sensor may be useful in this app., but
again, I've never used one (just know how they work).

Best Regards,

Vincent Deno