Will these trigger a check engine light after install?

No — these are OEM-spec sensors that your ECU recognizes immediately. Once installed at factory mounting points, the system reads them as original equipment and runs without fault codes.

Do I need to replace these as a pair or can I swap just one?

Both sensors monitor the same combustion process from opposite sides. Replacing only one creates a mismatch that throws off fuel trim calculations. Install both at once to keep your engine running balanced.

What tools are needed to swap these out?

Basic hand tools — socket set and wrenches for the sensor body. Your service manual will specify torque specs. No special diagnostic equipment required for installation; you're just unbolting old units and bolting new ones at the factory points.