Gearstill Glass

Squat sandglass in an iron cage, the sand inside a dull red, the frame worn bright where a thumb turns it.

Each charge, turned over, stops every wheel, gear, chain, weight, and spring within 30 feet for 15 minutes: mills, winches, portcullis drums, water screws, and mechanical traps hold exactly where they are and take no force in either direction. Living creatures are unaffected. When depleted the glass still measures a true quarter hour in any weather, current, or magic.