Add crab legs and sprinkle with Old Bay seasoning.
Close the lid; turn the knob to Sealing.
Press Manual or Pressure Cook button and adjust time to 1 minute, then press Pressure button and adjust to Low Pressure.
When the timer beeps, immediately turn the knob from Sealing to Venting, then remove the lid immediately. Overcooked crab is very flaky and not tender, so it must be removed from the heat source as soon as possible.
Remove crab to a plate and serve with butter and lemon.