The disposable lighter is a banned item on my airline since it is classed in the dangerous goods category. However, it doesn't set off the metal detector so how do you stop passengers carrying then on board?
Of course there is no reason to have matches, cigs, or lighters on board aircraft these days, but people will still carry these item in their pockets. They are not going to pack them into checked luggage just because they can't use them on board. For smokers, these items are classed as valuable goods, and as such remain in their possesion in much the same way as your car keys, passport or wallet remains in your possesion.
Since the reason disposable lighters are banned from aircraft cabins is a technical one rather than a terrorists one, security teams may not be aware of the ban.