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Comment by samwillis | Hacker News Reader

A really simple "hack" of a car park with an entry barrier that issues you a ticket is that you can usually exit the car park with an unpaid ticket if it's under 10 min old. So just get a new ticket from the entrance when you want to leave.

They do this so you can get out if there are no spaces.

I haven't done this myself and don't condone it. You will probably get in trouble and it's not nice.

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And let's add the legal term for it here, so it's clear what this "hack" actually is: Fraud.

A very relevant xkcd: https://xkcd.com/1494/.

> So just get a new ticket from the entrance

Getting a new ticket from the printer before the barrier will be hard if your car is inside the car park. Often the ticket printer will only work if it notices a large metal object (such as a car) in front of the barrier.

Many automated garages ban motorcycles because they're unable to trigger the sensor.

Or they make the barriers slightly shorter so that motorcycles can park for free.

Which they do, recognizing the fact that if there are a few motorcycles parked in your lot, it makes the whole lot look cooler.

Interestingly, I find that on my bicycle I can trigger the sensors in roads (which in the UK seem to be marked by a line of tar, where the sensor has been cut in and sealed up) by angling my front wheel directly along the line - my belief is that it gives a pretty strong signal because the rim of the wheel is a lot closer than a car would be even though they are a heavier chunk of metal (inverse square relationship). In fact my impression at one place I worked was that the sensor gave a stronger signal doing this as the barrier to get out went up quicker for me than it did for cars. I have extrapolated this belief and also believe that the sensors that detect vehicles before traffic lights also give a stronger signal when the rim is close by and the lights choose to turn my way quicker as they think I'm a bus. I can't really verify this though, because I only ever travel by bicycle.

Anyway, I guess motorcycles are not quite as maneuverable as a bicycle, so would find it harder to trigger the sensors in this deliberate way.

The trigger for lights in the states is electromagnetic. A lot of bikes don't produce enough to trigger so placing a magnet on the frame below the bike helps get you through the lights quicker.

Not-All-That-Interesting-But-Relevant-Story-Time:

In Santa Barbara all of the parking lots downtown where the bars are had attendants. This was before people credit card machines allowed lots to be open 24/7. Anyways, most lots had the entrance/exits at the same location so if someone pulled in to get a ticket and then backed out the attendant would notice. One lot had the entrance all by itself on the opposite side of the lot, blocked by some trees. I have many friends who would go out for a night on the town and then get someone to drive them back in the morning, pick up a ticket without entering, then leave using that fresh ticket.

I've wondered about how hard it would be to fool those. Presumably it's a simple induction loop, so a suitably calibrated electromagnet should do it.

When I parked my motorcycle in the garage at my old job, occasionally, the mechanism did in fact fail to "see" my bike so the low tech solution was that the attendant had a hunk of metal with a handle that he/she would set on the pad when the gate failed to open for my bike.

I think this will not work with most of good systems. As there are inductor loops or sensors at the gate(ticketing machine) . Which sense a vehicle and then allow allow the machine to print a ticket. You should check your hypothesis.... But m sure there r weaker systems which don't have these checks

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