Safety system for elevator doors

A slide door system has a pair of horizontally opposed vertical frame portions (42), upper and lower vertically opposed horizontal frame portions (44, 46) connecting uppermost, lowermost ends of the vertical frame portions (42) respectively, the opposed vertical and horizontal frame portions (42, 44, 46) defining an opening therein, and a slide door (38) moving horizontally to open and close the opening, and'comprises: a first optical device (78) having a light emitter (88) for emitting light and a second optical device (80) having a light detector (90) for detecting the light emitted from the light emitter (88), wherein one of the first and second optical devices (78) is positioned in one of the opposed vertical frame portions (42) and the other of the first and second optical devices (80) is positioned in the upper horizontal frame portion (46) and adjacent to the one vertical frame portion (42), so that the light from the first optical device (78) travels toward second optical device (80) along a gap (72) defined between the slide door (38) and the one vertical frame portion (42).