You can use this to detonate a sonic grenade, firework, lights, anything! Super cheap and reliable, $5 project.
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Step 1: Get your materials

-Depending on what you want to do, I suggest you pickup an alarm clock (with sound) or kitchen timer. Both were $1 at Dollarama!

Step 2: What to detonate?

I picked up a 90dB window alarm, and was going to use that for a sonic grenade, then I found a 105dB personal alarm, and decided it would be better!

Step 3: Building.

-This is where the fun starts, smash open the clock and the and locate the wires running to the tiny alarm speaker.
-This will be a low voltage out put so you will have to connect those wires through a relay to allow a higher voltage (usually 4.5V) to be sent to the personal alarm. otherwise it will not be loud enough.
-Carefully smash open the alarm (you will need to preserve part of the case, because the speaker needs to vibrate in it to amplify the noise)
connect the wires to the alarm speaker to the relay (note the correct polarity)

This is pretty much it, set the alarm clock to go off at a certain time, and its output will be sent to the relay, which will set off the alarm!!! This makes a great alarm clock for someone that doesnt like to wake up!!!

Step 4: Optional

Of course you could have used the timer if you wanted to make a count-down detonater... and instead of an alarm at the end of the relay, how bout an explosive?

Get some nichrome wire, and thread it through a safety fuse, and connect the wire to the relay, for a more detailed how-to on electrical igniters visit UN:
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Aron3132 years ago
Thats cool! I used a cell phone to detonate mine. I made it so that when you call it sets off the firework!
Should I just buy any type of alarm clock, what gauge nichrome wire would be perfect, do I need a specific kind of relay or is there a basic relay that would would work on any design. By the way I want to use fireworks instead of a personal alarm.
bighead54543 years ago
Would it be possible to change what is played when the alarm goes off? Such as changing it to sound an explosion for a prop?
weezee024 years ago
can i connect the alarm clock to a voice recorder so that whenever i set an alarm, it will playback my voice? thanks in advance, it is for our thesis.
gedion40005 years ago
I have a timer much like this one but when the alarm goes off it beeps, its not a continuous sound, will the current from the short beeps be enough to activate the relay? or does it need to be constant. i want a count down timer to power a relay to fire off a confetti cannon. i was hoping to use an electromechanical relay for its looks, but is there another one that might work better?
matt (author)  gedion40005 years ago
If your sound input is not continuous use a latching relay. This is essentially a flip-flop and a relay combination. Did you already buy relays?
gedion4000 matt5 years ago
no i haven't gotten relays yet. i had actually looked at the latching relay option late last night. from what i can tell you need the charges to be reversed in order to turn it off again, any suggestions on that aspect? i was also not sure of how much input they typically need to switch. the alarm i currently have sweeps from .45 volts to .27 volts. about every second or so, but it beeps really fast so i think my meeter is a little to slow to get a super accurate reading.
matt (author)  gedion40005 years ago
There are many relays available. If you cant find one that has a very low turn on voltage, then buy a transistor with a low threshold voltage, or a low voltage relay. And have it connect a source that has voltage high enough to trigger your latching relay. Then your circuit will look like this: Timer signal--> transistor --> latching relay Yes reverse voltage is needed to switch the latching relay. But for your application, a one time firing confetti gun, nothing matters after its been fired. Just disconnect the power to the circuit and then use it again.
jpoopdog matt4 years ago
heres a better idea, use a signal relay, with the source current (the sound output), passing through a low current high voltage (e.g A23, 12v) battery. signal relays can turn on high voltages with extremely low currents, such as mine which can turn on up to 15V 5A, using a current at least 5V 5ua (thats the next lowest form of miliamps), which is 0.005 or so miliamps. i have tested this instructable with my signal relays and they work fine, i also discoverd, with my cheap digital alarm clock, that on the microprocesor, or whatever the long black thing with all the pins has (i forgto the name), i remember if i shorted the first and second pins on one side while the alarm went off, or begun it with shorted, the alarm beep would be contant, and oddly become increasingly loud also, but only for 20seconds before it stoped.
gedion4000 matt5 years ago
thanks Matt, i didn't think about using a transistor to fire the relay, ill have to work something out like that if i cant find the right latch. i will also have to figure out some kind of switch to reverse the voltage, the cannon needs to be reset within a few minuets to be used over and over again
matt (author)  gedion40005 years ago
Heres an idea for the reset switch: From your battery source run a line, that goes through a push button, and a diode to your relay (make sure its reverse polarity). Then the button will be used to reset it. Also put a diode on the output from the transistor. The diodes will prevent the reverse voltage from going into and damaging your transistor and your power source. Good luck, let me know how you make out.
gedion4000 matt5 years ago
thanks, ill let you know how it goes.
tdwp11224 years ago
I don't know jack about relays-where did you get it and what type is it?
google it
nturner4 years ago
 how do you wire the relay? and can you use the same concept on a two way radio speaker for a detonator? 
akinich4 years ago
dude i have the same alarm clock
i opened it up and the wire came of from the solder joint
i need ur help
Minifig6664 years ago
 Leave this thing by the side of the road and the bomb squad will be all over it in second.
dodo1014 years ago
check my kitchen timer video:
tcm845 years ago
Wow! That purple touch sensitive explosive glued to the speaker is really great idea!
jsaul25 years ago
Cool idea--- I'd like to use the guts of a digital, or even analog alarm clock to rig an old portable record player to work as a bedside alarm clock. This would have a record play as a wake-up in the morning... I think it may be a bit more complicated to rig the alarm circuit for this, as the device should still have an on/off switch for normal operation, plus an alarm activated "on." Not sure how to go about any of it- this would be my first such project. Any advice or ideas?
russiankid5 years ago
well in the picture u dont have a seprate battery for the higher voltage of the personal alarm and that that doesnt look like relay can u help out
Lance Mt.5 years ago
Hehehehe, although its not the most original i always had some fun with it when i was younger
Draco69735 years ago
In this photo you can clearly see a resistor- the dark, cylinder at the top/left -and a small transistor- a smaller dark shape- just below and right of the resistor. It is helpful for you to know the function of these components and how to connect them to accomplish the desired outcome of this Instructable. Don't give up! It can be done!
e-vad5 years ago
ok.. i am kinda new to this stuff. and i have worked with some basic wiring but when it comes to a relay i have no clue, so could some one maybe make an instructable or just tell me where to hook the wires up and where they are coming from.
matt (author)  e-vad5 years ago
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Take the battery out?
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A Safety Switch; It's easy to build a switch which MUST be held at angle or it won't fire. Most modern heaters have this mechanism in them, you could steal one from Mom's bathroom portable heater lol, just don't be shocked when it then falls over and burns the house down... It's probably easier to build a contact which to cut the power to the main timer / detonator if the unit falls over. Alternatively, and very VERY cheap, would be to take a reed switch, ( you can make from a tin can ) with springs to keep the switch closed. Then take a plastic "shim" or "connection barrier" and slide it between the reed switch contacts... attach a length of fishing line or twine and the thing can't go off until you pull the plastic "safety" off and activate the circuitry. This allows you to GET AWAY FROM THE DEVICE.
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Frogie, You are Right. SAFETY is paramount. This is only a 2nd backup safety switch... the real important switch would be an "Attitude Switch" to stop the timer if the "project" fell over or otherwise got out of true 90 degrees. I just made one out of an "Airborne" bottle... and a lead ball 1/2" and two wires, some electrical tape. It triggers at 50 degrees tip. This makes it possible to have a non vertical launch without mods... but it triggers well dead on at 50 degrees. I'll try to post an instructable but the bloody Airborne bottles have changed... now they have a snap on cap! :—(
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You need to check out the Australian Bottle Rocket gang...

These folks have spent a lot of time making Rockets work.
Or that...
I'd say running away would do pretty well heh.
You could add a switch to the circuit and just turn it off. (I think...)
i'd like the alarm to throw a 24 volt sprinkler valve. anyone know how?
Hi... You need a relay to fire the 24 v. circuit which can be triggered by the small voltage coming out of the speaker terminals. You would hook the Relay between 3- 9v. batteries connected in parallel and then to your sprinkler valve, using the timer / relay to fire the valve.

This relay from Radio Shack should do nicely.
The batteries, while DC, work fine with the AC Sprinkler valves, Just don't hold the button down too long or it could burn out the wiring in the Valve.
thanks a million!
Sure... I tried to send a diagram but something about formatting stopped it. Good luck and BE SAFE! Mark
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