Passive vs Active RFID

OK, this is not really arduino-specific but it can certainly be useful to someone. I'm trying to make a proximity-based keyless lock/unlock system for my computer :smiley:

I'm looking to a medium-range active RFID solution, basically not more than 1 meters (3 feet). As far as I understand, the main difference with passive RFID is that the tag is powered, thus sending out an ID signal at a regular interval. What I am not sure, though, is if you can use a regular passive transceiver, or a special one must be employed?

Or, should I be looking into building a higher gain transceiver antenna and sticking with regular passive tags? This would actually be preferable as I'd like to use those credit-card tags and keep it in my wallet (not quite ready for skin implantation yet ;D)

So... any insight would be appreciated :slight_smile:

Just to clarify, as my first reading sounded like you had it backwards. I think you have it right. Active is powered, and emits IDs. Passive is... well... passive. It doesn't do anything unless you scan for it. The RF energy of the scanner's challenge signal is absorbed and powers the passive tag enough for it to reflect back a response signal.

Generally, passive is only useful for knowing when a tag is being carried past a known location, such as passports and border guards, or merchandise and shoplifting gates. Active is useful for finding objects that don't move around much, or move without limits in a wide area.

All the active tags I've seen are quite large in comparison to passive, as well.

Since your key will be brought to the door, I see no reason to go to active tags.

The main problem is range. Off-the-shelf passive solutions that can easily integrate with an arduino only have a range of about 3 inches maximum. So unless I stick the antenna on my chair, it will not reach far enough.

What's promising is this, Gen 2 passive equipment:

Basically with a range of about 3 meters for the credit card tags. But the readers, at least on that site, are pretty fancy/heavy duty. I'm gonna send them an email and see what they can recommend.