The most critical details to record for each hardware item in an asset inventory are the serial number, model, location, and ownership. The serial number uniquely identifies the hardware, crucial for tracking and validating warranty claims. The model helps in assessing compatibility and maintenance needs; the recorded location aids in managing physical security and efficient troubleshooting, and ownership details specify accountability. While 'MAC address, vendor, and maintenance schedule' seems plausible, MAC addresses and vendors provide limited information beyond network configuration needs, and maintenance schedules, though useful, do not directly relate to asset identification and security control.