Security Gremlin
Wondrous Item,
Common
(cost 100 gp)
Crafting Components
Armor sized for a Tiny creature
This military-styled tin contains a Tiny ethereal mottled green goblinoid dressed in soldier’s armor and when opened it salutes with earnest eagerness. You can instruct this gremlin to patrol an area, such as the perimeter of a room, campsite, or structure, while keeping watch for a creature type you instruct it to watch for. It completely ignores any creatures that are not of the chosen creature type. If it spots a creature of the chosen type, it immediately begins shouting loud enough to be heard within 30 feet as it runs back into its tin to hide.
Source