Click here for Wookieepedia's article on the Canon version of this subject.  This article covers the Legends version of this subject. 

OnALegendsArticleGoToCanon

A toxin detector was a small handheld device that could scan food and drink to determine if it was spoiled or poisoned. It could provide a visual indication via a blinking green light if the item scanned was safe for consumption. It could also be set to vibrate when a poison was detected. A more expensive model was concealed in a bracelet or other piece of jewelry for maximum concealability.

Sources