The label on Off Clip-on Mosquito Repellent, $10, claims "head to toe protection up to 12 hours." The device, which uses a fan to circulate repellent, attaches to a waistband, belt, or purse. It's approved as a spatial repellent (not for skin). Its active ingredient is metofluthrin, a neurotoxin. The label says, "Avoid breathing vapor," but it's hard to imagine how, with the repellent swirling around you.
We attached Off Clip-on repellent to the waists of four testers for 12 minutes every hour and sent them one at a time into screened enclosures with 1,000 hungry, disease-free mosquitoes. (We added 500 new mosquitoes for each tester's subsequent session.) Between sessions, we kept the devices running but stored them away from the testers and enclosures.
Ouch. Although Off Clip-on initially reduced the number of mosquitoes near our testers, two of them still received one bite each during their first session. That's far less protection than the 7-plus hours of complete protection we've seen with many skin-applied repellents. By the third session (2 hours after the device was activated), we had stopped testing on all four subjects because of bites. Instead of clipping on this Off device, consider buying one of the highly rated sprays from our recent tests: Off Deep Woods Sportsmen II, Cutter Backwoods Unscented, Off Family Care Smooth & Dry, 3M Ultrathon (all with deet); Repel Plant Based Lemon Eucalyptus; or Natrapel 8-Hour with picaridin.