Safety Alarm Clock




I often find getting out of bed in the morning a bit tricky. When i have somewhere to be at a certain time, i get up pretty reliable. However when I want to get up it always seems that I manage to turn off my alarm clock before fully waking up.

Put it on the other side of the room? Multiple alarms? Sooner or later I acclimatise, and fall back to old habits...

This instructable will hopefully show you how to put your alarm under lock and key! This is the safety alarm clock.

Step 1: Things You Need

The chart below, I think does justice to the battle between my sensible conscious mind who wants to get up and do stuff and the selfish sleepy one who only wants to lie in bed.

The main point of my alarm hack was only to allow control of the alarm clock to me once the critical time had passed, once the sensible me was in control... I want the selfish sleepy me to be locked out of any alarm turning off privileges!

Things you will need

Cheapo digital alarm clock Get one with a back up battery if you want to do steps 6-8

Wire Cutters
Screwdriver to open alarm clock
Soldering iron
Wire ( double insulated core and jumper)
Project Box
Heatshrink/electrical tape
SPST Key switch (available from maplins for �3 in the UK!!!!)

for making the clock unpluggable you will need
a 2N3904 transistor
buzzer (6 - 12V)

got all these? no? doesn't matter, the only thing you really need for this is the key switch and alarm clock the rest I'm sure you can improvise!

Step 2: Open Up Your Alarm Clock

Before you open the sucker up, find out the specifics to control the alarm. For instance on my clock the alarm would not go off when the snooze was depressed, would be reset by the alarm set button etc... Try to figure out a way to the control the alarm on and off with a only a single switch.

WARNING : This may be a mains operated device, make sure you unplug it from the wall before even looking at a screwdriver!!! To be extra safe, leave it overnight uplugged to let capacitors discharge etc...

Looking inside it should be a tangled mess of wires, circuit boards and other such electrical jetsam. Don't be scared because most of that stuff is not important.

Now you need to find access points to the various buttons and switches that control you alarm. You want to try and figure a way of using one and only one switch to turn the alarm on or off.

Step 3: Wiring

For my clock I saw that all of the buttons that had any influence on the alarm shared a common ground! If your clock is based on any sort of microprocessor, this will probably also be the case. Even if the relevan buttons are far apart, you may be able to find a common ground point for them.

you can use a multimeter which has a continuity mode to test if two points on the circuit are connected. Or if no continuity mode, measure resistance, low resistance (ie zero) means a connection.

Step 4: Modifications

The solution for me was to put the key switch (more on this later) in series on the common ground, I would also lam the switch on the side so that it was stuck on the alarm on position. to make sure that the alarm was not on every day, I shorted the button for the snooze.

This means that with the key switch open the alarm will go off, and only connecting the common ground with the key switch turns it off.

Step 5: Key Switch

I had seen these key switches in maplins a few months ago and thought I must try to get them into a project. A SPST cost only 3 pounds!!! It is basically an isolated switch that can only be changed by inserting and turning the correct key. A SPST switch has two positions, connected and unconnected.

Drill some appropriate holes in a project box or other container to house the key switch. If your alarm clock has enough dead space, you mount the switch on the body. Mine didn't, so i had to mount as a peripheral.

add another hole to your alarm clock to thread out the wire from the common ground, adding a knot before you leave, to make sure no stress is put on the connections themselves.

Thread the wire into your project box (adding another knot) and hook it up to the solder pots on the switch. I added some super glue to the bolt, key chassis, project box connection to make it extra sturdy.

Step 6: Unplugging

The clock still has a weak point. When you unplug it, the alarm dies... I wanted a way to remedy this situation without resorting to dangerously fixing the plug in the wall...

Now this clock has a back up battery which preserves the clock settings when it is unplugged. I broke out my multimeter to measure the current coming from the battery when the clock is plugged in and unplugged.

A small 0.3mA current when plugged in, and a large 2.3mA current when unplugged. I wonder if i could use that change in current to switch another componant?

Step 7: Transistorise

Transistors are great at controlling a large current by a small current. In this case I will use an NPN transistor to allow current to pass to a buzzer when the clock is unplugged.

Under normal conditions the current drawn by the clock is insufficient to allow any current to flow C to E and so the buzzer is silent.

When 2.3mA is drawn by the clock, the circuit is effectively opened between C and E, and so the buzzer can sound!

Step 8: More Wiring

Wiring up the schematic in the previous page was a little tricky... since it was all inside the clock.

I used crocodile clips whenever i was soldering the leads of the transistor. they can be pretty sensitive to heat, and the crocodile clip serves as a heat sink safety net for you.

I wrapped all the exposed joints with electrical tape and cut an extra slot around the rim of the clock so that the buzzer could go outside. If there is spare real estate inside your clock you can leave it inside, there wasn't in mine...)

If you hold the transistor with the flat face towards you, the leads from left to right are emitter, base and collector.

If you want to check that everything has worked before putting it together, be cafeful. Plugging and unplugging whilst the case is open is potentially lethal. don't touch anything inside if you plug in the clock.

Step 9: Put It All Together!

Hopefully everything should go back together nice and snug.

Set the alarm, turn the lights out, chuck the key somewhere in the dark and fall asleep confident in the knowledge that the time you set on the alarm will be the time the you get up!



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    86 Discussions


    10 years ago on Introduction

    this is cool... but what if i hear the alarm and walk to the living room and fall asleep on the couch?

    5 replies

    Reply 10 years ago on Introduction

    yea that would work. but the problem is i would shut off the alarm and fall asleep again


    Reply 10 years ago on Introduction

    Well...someone suggested having a bunch of keys that look the same - get 20 or so keys that are identical by quick glance and put them all into a bowl. Before you go to bed put the real key into the bowl and shake it up. I doubt you'll go to sleep after trying out a dozen or so keys. If you still do then you might have to look into a medical solution o.o;


    6 years ago

    Made a compact version with a cheap travel alarm clock. It's been great so far :)

    2013 22:34.jpg

    10 years ago on Introduction

    If you need to get up, set the alarm, hear it and get up. Not too hard. Or ask your Mommy to wake you up. Or your spouse......

    3 replies
    jules15adam 101

    Reply 8 years ago on Introduction

    yea for real.. its like you have no control over your mind that early in the morning


    8 years ago on Step 7

    So when you unplug the clock the buzzer goes off alarming you that the clock has been unplugged or when you unplug the clock the buzzer goes off when he has to, just like when the clock is plugged? This is a very awesome idea!


    8 years ago on Introduction

    Those who do not suffer from the dreaded sleep monster ( Z monster) have no idea how difficult it can be to shake the seratonin, melatonin induced coma from the brain.

    This is a nifty idea. I also like the clocks that start lighting up the room 15 minutes early and by the time the alarm goes off they are fully bright.

    Ceiling cat

    8 years ago on Introduction

    I think it would be a good idea to run a longer wire for the key box to another room so that you need to get up, walk to another room, and turn it off. That way the walking will help wake you up, and you can't just keep the key next to the clock and turn it off and go back to sleep.


    9 years ago on Introduction

    would be a great idea if it wasnt easier to just glue or take the snooze button off?

    adam 101

    9 years ago on Step 9

    Couldn't a wire cutter and/or wire stripper render the clock turnoffable?


    9 years ago on Introduction

    What YOU need is the "sonic bomb" alarm clock. My friend has REAL trouble getting up so he bought this. It sounds the alarm at an ear piercing 130 decibels! That's louder than a helicopter at take off! It also has a mini padded bass speaker which you put under your pillow.

    1 reply