Prime time’s longest case of unrequited love may resolve itself as “Ed” (8 p.m., NBC) wraps up its third season. Ed’s (Tom Cavanagh) growing affection for fellow barrister Frankie (Sabrina Lloyd) forces Carol to snap out of it and finally make a move to win back her dithering man. But can she move fast enough to save “Ed” from cancellation?

It’s never a good sign when shows wrap up their seasons before May sweeps. NBC probably won’t announce its decision to renew or cancel this series before then. For what it’s worth, I think tonight is the swan song for “Ed.” The genial series never attracted a large audience, and its recent move to Friday night has not changed that fact. “Providence” consistently got better numbers than “Ed” and it didn’t survive.

• You never know where Shannen Doherty will pop up next. The former “Beverly Hills 90210” bad girl is host of the new prank reality series “Scare Tactics” (9 p.m., Sci Fi). “Tactics” presents the hidden-camera antics of “Candid Camera” with a decidedly spooky sci-fi twist.

In each mercifully short segment, sneaky accomplices fool their friends into scary scenarios. For starters, a couple are invited to a rave party in the desert when they see a blinding light on a hillside. Their car suddenly stops and its instrument panel goes haywire. Then, without warning, a 10-foot monster attacks them and rips the driver-side door off the car, taking the driver with it. The camera work has all of the shaky hand-held hysteria that made “The Blair Witch Project” simultaneously frightening and stomach-churning.

The makers of “Scare Tactics” are wise to choose younger participants — some of these stunts could result in a coronary. “Scare Tactics” is dumb in all the best ways. It’s also different, desperate and diverting.

• What do the rich, almost rich and semi-famous do on their down time? Do you care? The makers of “Celebrity Hobbies” (7:30 p.m., DIY) do. Who knew that Sammy Hagar liked to cook with tequila? Or that Fabio spends his time and money building a collection of motorcycles?

FYI, the DIY network is a sister network of HGTV. And “Celebrity Hobbies” is hosted by Tracy Griffith, the half-sister of Melanie.

Tonight’s other highlights

• Mario Lopez is host of “America’s Most Talented Kid” (7 p.m., NBC).
• Tommy Lee and Naomi Campbell guest star on “Fastlane” (7 p.m., Fox).
• A customs agent (Stephen Baldwin) catches bad guys among the skydiving subculture in the 2000 thriller “Cutaway” (7 p.m., UPN).
• James Woods plays New York’s controversial mayor in the 2003 biopic “Rudy: The Rudy Giuliani Story” (7 p.m., USA). The network recently announced that this was its highest-rated movie since “Atilla.” Who says viewers don’t respond to tough guys?
• A recent murder reminds Mike of a 5-year-old case on “Hack” (8 p.m., CBS).
• A mass-murderer targets the rich on “Law & Order: Special Victims Unit” (9 p.m., NBC).

Series notes

Arsenio Hall is host of “Star Search” (7 p.m., CBS) … Tom Bergeron is host of “America’s Funniest Home Videos” (7 p.m., ABC) … Office gossip on “What I Like About You” (7:30 p.m., WB) … David dates on the rebound on “Greetings from Tucson” (7:30 p.m., WB).

Lightning short-circuits John’s genius on “John Doe” (8 p.m., Fox) … Paul hits it off with his editor on “8 Simple Rules” (8 p.m., ABC) … An awkward double-date on “Reba” (8 p.m., WB) … Claudia vetoes Sean’s new hire on “Grounded for Life” (8:30 p.m., WB) … Joe frets about losing touch with his family on “Regular Joe” (8:30 p.m., ABC).