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An even more evil version, dated early 80s or even earlier, used cmos counters and gates to make a piezo buzzer emit a cricket like sound (1). The evil touch was adding a photoresistor and a timer circuit, so that it kept inactive until there was dark, then it waited for like 10 minutes and started chirping, only to stop immediately as long as someone would turn on the lights. That made it the best prank to hide in someone's dorm room: super hard to locate and awfully annoying:)

(1) a realistic cricket chirp can be made by driving an oscillator using 3 or more outputs of a binary divider; a cd4060 could be used alone by setting the internal oscillator to a few KHz frequency, then sending it to an amp (bjt, mosfet etc) keyed combining some of the 4060 binary divider outputs, so that the continuous tone becomes an intermittent chirp.

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This is quite possibly the most evil benign prank I've ever seen. I'd like to give a wink and a finger gun point to the person who thought of this. Are there other things like this that one could do to spice things up at the office? I like pranks like this where nobody gets hurt physically.

My all time favorite prank is getting harder to do but it is still possible.

Back in the day, most people had full size umbrellas. When it looked like rain in the morning, they would take their umbrella in to work and hang it by the handle on the wall of their cubicle.

I would loosen the umbrella (partially open while holding upside down), put hole punch chad in the umbrella, and then re-close the umbrella and hang it back up.

If it was raining at the end of the day, you knew you got the victim by the hole punch chad at the door. :-D If it wasn't raining, you knew it was just a matter of time. :-D

With the compact umbrellas, it is harder to get access to sneak chads into them and hole punch chad is somewhat harder to come by.

I haven't been this excited to talk about Chads since the election, this was a pleasure to read!

>I like pranks like this where nobody gets hurt physically.

I'd rather get punched in the face and get it over with than endure this.

"Are there other things like this that one could do to spice things up at the office?"

There was a variation on keyloggers disguised as USB hubs used to sniff passwords and text, basically a man in the middle attack on keyboards. They're essentially read only devices which store what they sniff into internal memory or retransmit it using other means. They however could be reprogrammed not to spy but just to emit certain text appended or in place of what comes from the keyboard, possibly in a spectacular way like waiting for a sentence written by the victim, then sending N backspaces to delete it and swapping it with a new one. ...who you gonna call? :)

If you think keeping someone awake all night against their will is "benign", please stay the hell away from me.

"Neighbor's house alarm triggers when I put my car in reverse" | https://news.ycombinator.com/item?id=15947540

>mindcrime: This seems like a particularly evil variation of that idea:

http://www.goldmine-elec-products.com/prodinfo.asp?number=C6...

Electronic Cricket Kit $5.75; min $10 order + at least ~$7.20 shipping (U.S.)

I actually have one of these on my desk at work, showing the youngsters what we did "back in the day." I made it when I was in college in the 80s (yeah, I'm old fart).

My first version was built with the classic 556 timer chip - you can still find schematics of this on the web.

The one on my desk is my second version. I did the circuitry, taped out and etched the circuit board, and assembled it in a small box. I have long ago lost the schematic so I need to reverse engineer it.

Chips:

* 4049 inverter - used as a 6KHz oscillator and probably the photoresistor sensor buffer for gating.

* (2) 4020 2^14 dividers => divide by 2^28: 6000 / 2^28 =~ 12 hours

* Battery and jumper.

12 hours before activation time (say 3:00PM), you connect power with the jumper. Sometime in the evening, you visit the victim and leave the "present." In the middle of the night it activates.

I'm a much nicer person nowadays. ;-)

Elektor magazine ran a schematic back in the 80's, it was also part of the Radio Shack 150 in one kit.

They're sold as kits:

https://www.amazon.com/Velleman-MK104-Electronic-Cricket/dp/...

If you're locating a chirper by sound, you're not seriously impaired by the lights being out.

Also, you could use a spotlight. If you shine the spotlight somewhere and the chirp stops or changes, search that area.

I think you’re assuming too much from the description. In order to be evil, when it’s chirping, the chirps are many minutes apart, not continuous.

That's the main factor then.

If you're relying on sight to find it, then it's irrelevant whether it makes a sound.

If you're relying on sound, you're impeded by the infrequent occurrence. That's would still be the case if the chirping went on with the lights on.

If the chirping requires near total darkness, because then to search by sound you have to go through the trouble of covering the windows (with something more than the blinds or curtains, if there are any) or else you're restricted too searching by sound only in the night hours, and doing a visual sweep by day or lamplight.

(But then the device only chirps in near total darkness, it may be defeated by a relatively dim night light.)

It's very difficult to accurately locate the direction of a high pitched chirp sound. The frequency makes a ton of difference here.

This is only true of a periodic sound. This is because when the wavelength is smaller than the distance between the ears, there is aliasing in the phase information (ambiguity). However, the overall group delay is perceptible at the onset and cessation of the tone. That doesn't give you much time to latch on to the direction. At high frequencies, though, level differences are useful. You know which ear is facing that chirp and which isn't.

I've found that particularly high pitched sounds can bounce of hard/flat surfaces very well.

It is possible to find it with a bit of hardware like a microphone. Very easily by taking multiple level measurement and some multilateration.

It gets hard when there is more than one.

The problem with identifying it by ear is that you get already some 20-30 cm precision at best unless you've trained in echolocation like some blind people. For such a small device it could well be a whole room.

Ok. We'll get you to clear any further pranks so you can tell us what's funny before we go and do anything rash such as trying to have some fun.

Shut it all down guys, kazinator will take over from here.

What?

He's just saying it's not that hard to determine the location of a chirping sound.

Not whether it's funny or not.

Whoosh.

>If you're locating a chirper by sound, you're not seriously impaired by the lights being out.

Even if you're locating it by sound, you probably don't want to stumble around in the dark while you're trying to find it. So you turn on the lights, and you can't find it because it stopped chirping. Then after you turn off the lights, it starts back up, so you turn the lights back on, etc.

This is like hunting mosquitoes. You get a couple, turn the lights off, then lie down. Only to hear yet more mosquitoes.

It will stop chirping whether or not you turn on the lights, and then not chirp again for a number of minutes. Unless it is pitch dark, you're not really stumbling; people can find their way around in dark rooms. The searcher can reduce stumbling by tidying the room and possibly even removing some items such as chairs and whatever.

If they are doing those things, I’d say the prank was successful.

I never said the prank is unsuccessful, only that darkness doesn't make it harder to find something by ear. Hearing is hearing, sight is sight.

In the past, I have had a hard time finding by ear which switching power supply in a lab is giving off a squeal.

Seeing the power supplies was of no help; it might as well have been dark.

Basically the "off when the lights are on" aspect just confounds people initially when they don't know that this is the case. They hear something in the dark. They hear it beep again some time later, and then again. They turn on the lights to go looking for it. Unbeknownst to them, doing so deactivates it. It takes time to learn that the chirping is related to it being dark. Once they realize that, it makes next to no difference.

It's still not a bad prank without that embellishment.

Fair enough, you didn’t say that. I just think we disagree on how easy it would be to track this thing down in the dark.

I have a bearded dragon, so I know what it’s like to have loose crickets chirping in your house and having no idea where it’s coming from. Like others have said, the nature of the sound makes it harder to locate.

There should be an app that allows one to triangulate sound sources to locate these darn things ..

Not that hard to do: sample the sound using multiple microphones, discard anything after the first thing you get (usually they're misleading reflections), then measure the delay to build a map of vectors pointing to the object. The military already have devices using that principle to locate the sound source of a weapon firing to send it a bomb. The RF variant is also employed in air traffic control and to detect pirate radio transmissions and uses arrays of omnidirectional antennas just like this one: https://cdn.everythingrf.com/live/direction_finders_teaser_o... Although military smaller ones are usually protected from casual view using dome-like covers.

Never change, HN.

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