Jean, if you mean a red dot unfortunately the S&W sd9 isn't cut to accept a red dot. You can buy a plate that replaces the rear sights to add one. If you are asking about fiber optic sights for it then here's a link to a set from truglo that will fit. Hope this helps, link here..................... budsgunshop.com/product_info.php/products_id/60382/truglo+fiber+optic+sights+for+s%26w+m%26p

As the guys have mentioned, the SD9 is not Optic ready. Now, I'm not a fan of the dovetail adapter plates to add an optic. Personally, if it were me, I'd get an Optics ready pistol or, if you're really wanting this model Sd9, you can send the slide out to have it milled for any optic you'd like!!
Good luck!!

Hi Jean, unfortunately the S&W SD9 is not cut for Optics. You would need the Galloway Adapter (replaces the rear sight here : https://gallowayprecision.com/optic-mount-plate-for-smith-and-wesson-sd-and-sd-ve-pistols ---------- And this Sight Puller/Pusher Tool to make the job easy and can be done yourself : budsgunshop.com/product_info.php/products_id/28316/ncstar+vtuprs+universal+rear+sight+tool+steel -------- Cheers and stay safe!

Hi Jean, unfortunately, the SD9 is not optics ready. You can buy a mounting adapter plate separately, but you will need to remove the rear sight and use that dovetail. >>> https://gallowayprecision.com/optic-mount-plate-for-smith-and-wesson-sd-and-sd-ve-pistols .......This works with JPoint, Shield RMSc, Shield SMSc, Shield RMS2, Vortex Viper, Vortex Venom, Vortex Defender CCW, ADE RD3-003, ADE RD3-006A, ADE RD3-006B, ADE RD3-018 Spike, Holosun 507K, Holosun 407K, Romeo Zero, Docter/Noblex Sight C, Docter/Noblex sight 2+, Docter/Noblex sight III, Docter/Noblex QUICKsight 5.0 VR, Noblex Sight G, Burris Fastfire 2, Burris Fastfire 3, Delta Optical MiniDot, Delta Optical MiniDot II, Hawke Reflex 1×25, Sightmark Mini Shot Pro Spec, Sightmark Mini Shot M-Spec, Leica Tempus, MAKdot 1×25, Vector Optics SCRD-19II Frenzy 1x17x24, Creative XP GlassEagle HD, Riton MPR D2, Riton 3 Tactix MPRD, Swampfox Sentinal, HEX Dragonfly, HEX Wasp, Crimson Trace CT RAD Pro, Cyelee CALF V2, Cyelee CAT PRO, or Vomz Pilad 1×20. Stay safe & have a great day!