Sight Scope (サーチスコープ , Search Scope?) is an accessory in Chrono Trigger and Chrono Cross. How the item effects party members and where the item is found varies between games.
Chrono Trigger
While Sight Scope allows the wearer to view enemy's current/max HP, it does not work on bosses. Lucca is equipped with this accessory when she joins the party, but it can be worn by any character. The antannaed helmet Lucca wears in official artwork and in-game snapshots of Chrono Trigger is likely the Sight Scope.
Chrono Cross
Able to be worn by any character, this accessory increases hit rate by 3%. It can be disassembled for one 1 Copper and 2 Fur or sold for 380 G. Commonly, this accessory can be stolen from Polly and Cassowary (Home World). Rarely, it can be stolen from Gremlin, Lava-Boy (Another World), and Mannequeen. It can be found in a chest atop the balcony of Viper Manor (Another World), which, coincidentally, is near the spot where Luccia is recruited, Luccia being a character almost identical in physical appearance and personality to Lucca.