Between 15 to 20 ghost seekers show up for nightly San Antonio tours, which run an hour and a half and cost $10 for adults, reports Martin Leal, Alamo City Paranormal's owner. A favorite part of the tour, Leal says, is when the tourists get to play around with the ghost detectors for 20 minutes or so. Leal says revenues, which have been flattish for years, grew 21% in 2004. He's now trying to take his association of a dozen local companies charging for ghost-hunting services, called the American Alliance of Professional Ghost Hunters, nationwide.

Considered the Jaguar of ghost detectors is AlphaLab's TriField Natural EM Meter, selling for around $300 and measuring magnetic, radio-wave, and electric-field changes. The company, which sells about 200 such detectors a year, is considering making a detector that can draw an image based on the changes in the electromagnetic field it's detecting, says CEO David Lee, who has a Ph.D. in physics. Lee says he doesn't believe in ghosts but is undecided on the existence of UFOs.