West Yorkshire Police has admitted one of its Taser weapons has gone missing and appealed to the public for information on its whereabouts.
The force said an extensive search was under way for the stun gun, used by police to deliver an electric shock.
It has gone missing from a storage unit at the force's Leeds training ground.
A spokesman said it was likely to still be on police premises, but a public appeal was being made "on the off-chance" anyone had information.
The Taser was being used for training purposes, he added.
The spokesman said: "It is very likely the training Taser's battery is now inert and unable to be discharged.
"We would like to remind the public it is a prohibited weapon and as such it is illegal for a member of the public to possess one."