If we mix and match wireless tech - 100m with passive RFID is possible.
Johns well researched answer covers all of the basics and I'm not going to duplicate his work or references (as hard-science doesnt forbid building on other answers), but he shows:
- Passive RFID (no battery in the card) can transmit 10m.
- Active RFID (where the card has a tiny little battery to help with power) can transmit 100m.
The question excludes active RFID and demands no on board power. So we need a way to charge up the rfid transmitter's capacitors to store enough power to get the range of an active rfid tag without relying on an on board battery.
I think the best way to do this is have them constantly trickle charging the capacitors from a remote power source of some kind. And I mean trickle - these power over distance calculations come out in microWatts. Pretty useless for on demand transmission requiring 10000 times that, unless the crowd is willing to wait a few hours for their rfid transmitters to charge while the cop scans them.
Look into research for power over wifi, in which devices can be charged using idle spectrum from a household 2.4ghz wifi router. This requires the router to detect and charge the card, and the user to opt into that behavior in the settings, even if it also charges the users phone wirelessly in your pocket (and most people opt in due to that convience), it may not be 1984 enough for your needs.
In which case your more interested in the later parts of that linked article, in which they're able to utilise the TV signal from a tower 10km away to trickle charge a tiny device.
So the secret is to have 3 devices
- A big antenna that trickle charges every card in town at a rate of microwatts, but a range of several km. Looks like a large TV tower mounted on a hill. May actually also broadcast real TV.
- The card in peoples wallet that discretely hides the rfid chip is trickle charged passively by the large antenna.
- The agent uses a handheld device to contact all the the tags, the tags then respond, using the capacitors (that have probably been on charge non stop since manufacture) to boost their signal such that it can travel ~100m and penetrate some thin walls.