The E3T-SL24 is a miniature square convergent-reflective photoelectric sensor with a PNP output — one of the tighter-focus parts in Omron's E3T line. It's sized for small spaces: a compact square body that fits where a big barrel sensor won't, and a pinpoint red LED (650 nm) that hits a 50×50 mm white target from 5 to 30 mm out. Response time is a crisp 1 ms, so it'll handle fast small-part detection on a pick-and-place or label feed. Power it with 12-24 VDC, draw about 20 mA, and you get reverse-polarity and short-circuit protection built in — saves a fuse when the wiring hunch fails.
If you're cross-shopping the E3T-SL14, the headline difference is sensing reach and hysteresis. The SL24 reaches farther — 5-30 mm versus the SL14's 5-15 mm — but trades a wider hysteresis band: 6 mm max on the SL24 versus 2 mm on the SL14. That means the SL24 gives you more working room but needs a cleaner contrast between object and background to avoid false triggers on a near-miss. Both are PNP, same power and protection, same body style. If your application has a tight repeatability window and only needs 15 mm, the SL14 is the tighter choice. If you need that extra 15 mm of reach, this part.