ESN area protection is multi side protection or square meter protection safety light curtain, include 1pc emitter, 1pc receiver, mirrors and pillars depend on your request how many side to protect.  It utilize reflection theory of mirrors. Emitter send raw light to mirror, and reflect to receiver to form a 2 side or 3 side protection, when people cross into the intangible area, light of barrier is blocked and send signal to machine or alarm device to achieve a protection function