Sonic knife
From Tardis Wiki, the free Doctor Who reference
The sonic knife was a device that Scaroth planned to use to steal the Mona Lisa. It was capable of cutting through the glass case that was protecting the painting. (TV: City of Death) http://www.fantastic-original-doctor-who-props.co.uk/4th%20Doctor%20Items/Story%20105%20-%20City%20of%20Death/Props%20and%20Costumes/Story%20105%20-%20Romana's%20Tool.jpg
