What equipment was used to watch enemy in trenches?

In World War I, soldiers used a variety of equipment to observe enemies in trenches, including telescopes, periscopes, and binoculars. Periscopes allowed troops to see over the trench walls while remaining hidden. Observation posts equipped with telescopes were also set up to monitor enemy movements from a higher vantage point. Additionally, listening devices and observation balloons were employed to gather intelligence on enemy positions.