Tag Archives: trap

Door Bomb and Safety Catches

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Johnny leaves the airport by taxi, ending up in a disreputable part of town. During his ride we see another video phone call with a different interface, and the first brief appearance of some high tech binoculars. I’ll return to these later, for the moment skipping ahead to the last of the relatively simple and single-use physical gadgets.

Johnny finds the people he is supposed to meet in a deserted building but, as events are not proceeding as planned, he attaches another black box with glowing red status light to the outside of the door as he enters. Although it looks like the motion detector we saw earlier, this is a bomb.

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This is indeed a very bad neighbourhood of Newark. Inside are the same Yakuza from Beijing, who plan to remove Johnny’s head. There is a brief fight, which ends when Johnny uses his watch to detonate the bomb. It isn’t clear whether he pushes or rotates some control, but it is a single quick action.

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This demonstrates an interesting difference between interface design for the physical world and for software systems. Inside a computer, actions are just flipping bits in storage and thus easy to undo. Even supposedly destructive actions such as erasing files can often be reversed. In the real world, the effects of, for example, explosions tend to be much more permanent.

We generally don’t want destructive actions to be too easy to perform, from guns and other things that go boom to formatting computer disks.

A widely used solution in the real world is the safety catch, as with guns, or arming switch, seen in countless thriller films with nuclear weapons. Another example are the two-hand safety switches used in high voltage electrical distribution panels. Activation of these requires two individual actions, separated in time and at least a short distance in space. Some systems, both real and in film, go even further and have covers on the arming switches, so even just preparing for activation requires two separate physical actions.

While the bomb is on his belt, Johnny doesn’t have to worry about accidentally pressing the “explode” button on his watch because the bomb is not active. Only after he has armed it and placed on the door can the watch activate the bomb, so he can take his time and verify whether or not it is necessary before doing so. And when it is active, he can do so very quickly even though he is in the middle of a fight.

But safety catches and arming switches introduce modes to an interaction, which have a bad reputation in interface design. Had the watch-bomb designers followed most conventional GUI design guidelines, there would be no arming switch on the bomb. Instead the watch would have popped up a “Do you really want to explode the bomb (Y/N)?” dialog, possibly with a short delay to ensure Johnny thought about his decision before answering. He would have been decapitated.

Compare to LoTek

Later on in the film we see an example of a poorly designed system without a safety catch. The LoTeks in their bridge home have a defensive “bug dropper”, so called because it drops ancient Volkswagens from a great height.

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The bug dropper can be activated by pushing just a single handle. Because there is no safety switch, a guard accidentally drops a flaming VW Beetle onto the lead characters, nearly killing them.

Conclusion

From the description above it would seem that safety catches are the obvious solution. But of course it’s more complicated than that. Consider what would have happened if Johnny had met friends instead of enemies and settled down for a conversation. Thirty minutes later they’ve agreed on another meeting, and Johnny taps his watch to bring up the reminders app. Oops!

Should the bomb have disarmed itself after a given time period? If it did, how would Johnny be notified of this?

Most of us do not design interfaces for lethal hardware and life or death situations. There are however an increasing number of drones and other physical devices which are now remotely controlled from phone or tablet apps rather than dedicated hardware controllers as in the past. The “Internet of Things” will bring even more real world actions under computer interface control. In the future, we will most likely see more of these safety catches and arming switches in computer interfaces, and we need to figure out how to use them properly.

Ghost trap

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Once ghosts are bound by the streams from the Proton Packs, they can be trapped by a special trap. It has two parts: The trap itself, that is roughly the size of a toaster, and the foot pedal activation switch, which connects to the trap box by a long black cord.

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To open the trap, a ghostbuster simply steps on the foot pedal. For a second the trap sparks with some unknown energy and opens to reveal a supernatural light within. Once open, the bound ghost can be manipulated down towards the trap.

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When the ghost is close to the trap, the Ghostbuster steps on the foot pedal again. Lots of special effects later, the ghost gets sucked down into the trap and it closes.

With a ghost contained inside, a red indicator light illuminates near the handle to let users know that a dangerous thing is contained within. (Also, it emits smoke, but I suspect that’s a side effect rather than a feature that’s been added in.) The trap can be held by the long handle or (and this is the way the Ghostbusters themselves tend to carry it around) by the cord.

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The design of the trap has so many great aspects. The separate control keeps the ghostbuster a safe distance from both the proton streams, the trap, and the ghost. And the use of a foot pedal as a switch keeps his hands free to keep a defensive grip the proton gun. I should also make note of the industrial design of the thing: The safety stripes, the handle, and the shape tell of a device handmade by scientists that is dangerous and powerful.

Still, some improvements

If the activation was wireless rather than a foot pedal, the Ghostbuster would be free to move to wherever was most tactically sound, rather than constrained to standing near it. Wireless controls have their own tradeoffs, of course, and those may not be acceptable in the mission-critical scenarios of ghostbusting. If that control was also hands-free (gestural, vocal, ocular, brain) then you’d keep the goodness of the hands-free pedal.

The red light is a little ambiguous. It could just mean “power on,” which doesn’t help. Blinking should be used very judiciously, but here it’s warranted, so I’d make that blink to say “Dangerous thing contained. Release only with caution.” Let’s presume the thing automatically locks when a ghost is trapped and can only be unlocked by the containment unit (the next post). Even better might be several lights blinking, perhaps both around the trap doors and around any controls that might release the ghost, e.g. the foot pedal. You could even make it blink similarly to the “working” light animation of the Proton Packs to tie the equipment together.

One problem that’s familiar to software designers is that’s that the control is a stateless toggle, i.e. it looks and behaves the same whether you’re opening the trap or closing the trap. If the trap doesn’t automatically lock with a ghost in it, that’s a major problem. Imagine if the activator had hid behind a curtain to trap a poltergeist and wasn’t sure if he’d accidentally stepped on it. A UX 101 rule of thumb is that controls should indicate the state of the thing they’re controlling. So the pedal should have a signal to indicate whether the trap is open or closed, even though the trap itself conveys that pretty well. Even better if that signal is something that can be felt with the foot. Maybe it’s a rocker switch? (Like this Linemaster, but more exaggerated.)

Lastly, we can also presume that the trap has a power source, and that there’s a time pressure to get the trap to the containment unit before that power source dies. But where’s that information? So some indication somewhere of how much power and time is left for that would be very useful to avoid all that work (and, you know, property damage) going to waste.

Small improvements, but each would improve it and not take away from the narrative.