What is meant by an alarm clock here? It means something that will help you to see when you are being more mechanical, and remind you to make efforts to be less mechanical. Alarm clocks come in all shapes and sizes. They can be rather artificial, or very natural. The best ones tend to come from self observation, when you have seen something about yourself.
Sometimes alarm clock exercises are set, or you can set them for yourself. For example, if you brush your teeth with your right hand normally, try doing it with your left hand for a week. You'll probably find that you will to begin with always reach for the tooth brush with the right hand---and if you are awake enough to notice that, you can realise that you are behaving mechanically, like a machine, and make an effort to brush your teeth with more attention. Such exercises as this, using a different hand, or not saying a certain word, doing something different from usual, are useful for a short time, but they quickly become mechanical themselves, for example, in an exercise not to say a certain word, it can very quickly become mechanical not to say it, and then the exercise will no longer be any help in your aim to awaken.
I've found that in such exercises, it's much more effective to have a teacher set them for you. When I try and set them for myself, I have a tendency to lie to myself, for example, `I was going to start tomorrow', `I think another exercise would be better', or go on doing the exercise past when it becomes mechanical and useless, but feel `good' about how `well' I am doing it.
The above sort of exercise can be useful for anyone. It's also possible to find alarm clocks specific to yourself, for instance, you might observe that you use the word `can't' a lot. You could try observing how you use it. You may be a person who often says `can't' and limits their possibilities, when in fact, if you said `can' you would be able to achieve whatever it was you wanted to. You could use the word `can't' as an alarm clock. When you hear yourself say it, make an effort to be present. In my own case, an example is `surely', as an alarm clock for lying. Someone pointed out to me that when I started a sentence with `surely ' it was invariably to begin to say something that I had no proof of, from partial understanding of something, and was probably false. So, I tried to use this `surely' as an alarm clock. That doesn't mean I stopped saying it, it just means to try and be more awake, and ask myself `Am I lying now?' if I hear myself say it.
Examples with words are in the intellectual center. It's also possible to have alarm clocks in other centers. You may observe that certain habits in the moving center are related to your inner psychology, such as you may observe that you lift your hand to your mouth when you are about to lie.
These kind of alarm clocks might work really well for some people, but have no effect for others, since they are dependent on the individual's mechanics.
To find effective alarm clocks, you have to observe yourself and your mechanics. Also it's useful to work with other people, who can point out your mechanics to you, so you have something to look for in yourself. You also need to continually change the alarm clocks, as you'll quickly get used to them, and sleep through the alarm.