For instance, can I store both my car keys (a Lincoln MKZ) and my apartment door key on a single RFID microchip? I also want to use that same microchip to open my front door.
You are confusing some radio frequency identification terminology. An RFID tag is a transponder, which consists of a microchip attached to an antenna. Since the chip is part of the tag, you cannot have multiple tags on a single chip. I believe what you are asking is whether you can store several ID numbers on a single transponder and then use one ID to start your car and another to open your apartment door.
The answer to that question is no. Each transponder has a single unique ID. Some transponders contain user memory, and you could put whatever you wanted in user memory—and you might, if you were an electrical engineer, be able to build your own lock that would open your door if it read something in user memory. The downside is that anyone who knew the serial number could write that number to the memory of a different tag and then use that tag to open your door. Or they could use a device to emulate the tag and simply send repeated signals to the lock until hitting upon the correct string of numbers.
If you are an electrical engineer and you have the skills to create an RFID-enabled lock, a better solution might be to create your own lock that would open the apartment door if it read the serial number in the car key transponder. At least then you would know that your car key was likely unique, and that the lock would be a little more difficult to hack.
—Mark Roberti, Founder and Editor, RFID Journal
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