Sonic cane
From Tardis Wiki, the free Doctor Who reference
The sonic cane was a device used by the Eleventh Doctor to scan the Teselecta, and to contact Amy Pond and Rory Williams while they were miniaturised inside. Similar to the Eleventh Doctor's sonic screwdriver, the sonic cane emitted a green light. It recognised a signal from the sonic screwdriver as well. (DW: Let's Kill Hitler)
