Disabling people by disabling critical technology

People are dependent on technology. Disable a car, and the driver can be stranded in the middle of nowhere. Especially unpleasant in the areas where there's nothing but snow and mooses.

Modern cars are heavily dependent on electronics. An electric paralyzer, carefully applied to the vehicle control unit, and the car has to be towed. Alternatively, just steal the unit. One of the ways to steal cars with immobilizers is swapping the (externally accessible) control unit with another one with known codes.

Older, more classical way is water in gasoline tank. Stays at the bottom of the gasoline tank, gets pumped into the engine, and the engine won't run.
http://auto.howstuffworks.com/fuel-efficiency/fuel-consumption/sugar-in-gas-tank.htm

Emptying the car's tires is another classics.

There are efforts to develop devices to stop cars remotely, usually on the basis of microwave pulses. Discussed e.g. here:
http://tech.slashdot.org/article.pl?sid=07/11/13/2322241
An old car with a mechanical distributor will be immune against those; such vehicles are still to be seen in rural Finland.

An EMP/HERF weapon can be used also against fixed installations. I heard a hearsay about disabling security system by driving around the building with a minivan with plastic back (transparent for radio waves), and a surplus military transceiver with a directional antenna, keyed on and feeding the building with couple kilowatts of radio frequency waves. Reportedly there was a good chance that the security system bought the farm. But I heard it from somebody selling optical comm systems so it may have been marketing.

A cellphone with an attached relay can short out a power line and trip the breakers in a section of a building on command. This may be used as a method to disable the elevators on command, as I suggested earlier.

A rocket with an attached wire, fired from a building roof into a thunderstorm cloud, can attract a lightning into the building. Together with damaged grounding of the lightning rods, the electronics in the building may end up pretty fried. I thought about a high-tech variant, transforming the lightning energy to a directional microwave pulse aimed to a nearby facility.

A cellphone SIM card can be destroyed by powering the phone off (if on), on, then entering a wrong PIN for 5 times. Optionally then entering the wrong PUK 10 times (who remembers the PUK anyway?). Then the card is out of commission and the phone number is not working anymore until a new card is issued by the telco. A stranded person in the middle of nowhere, depending on the cellphone and without it, is out of action for at least hours.

For various wireless fun, not disabling but useful for gathering intelligence, check out my comments at Project WORM.