The Maintenance Keycard is one of several types of key-cards and is an important piece of equipment used for accessing the Holosprings Facility, especially through maintenance locations.
It is a mandatory piece of equipment in regards to progressing the Story in order to access what isn't tunneled in. The Holosprings Facility will not allow you to enter without the use of the Maintenance Keycard, and without it you will be locked to Maintenance Areas only. So long as you have the Keycard in your inventory, attempting to use any Keycard Scanner will automatically pull out the correct Keycard and hold it over the scanner. The Keycard Scanner will light up green and open the doors, which remain open for that save.
The Maintenance Keycard in appearance is a keycard sporting brown ends with a photo image and name of a "CARL PLANTER". It also features a barcode and the clearance designation of "Maintenance".