A Smarter Alarm with Events

Courses

• Grades 3-12

Materials

• Cellphone, tablet, or computer
• Internet connection

Educational Objectives

• Understand the concept of an event.
• Create a technological object (prototype) using a device.
• Identify relationships between technology and the surrounding world.
• Evaluate personal and others’ work.
• Engage in dialogue and reflection on improvement ideas.

Start (10 minutes) - A Smarter Way to Listen

1. Welcome students and introduce the day’s activity: “Today, we will learn how to create a simple alarm that plays a sound when you press a button, but using a new, smarter method.”
2. Start by asking the class: “How does a simple button or switch actually work?” Guide them to the idea of two states: ON and OFF.
3. Then, introduce the core concept for today: efficiency. Ask them, “Using a loop, our program has to constantly ask the button, ‘Are you pressed? Are you pressed?’. What if the button could just send a message to the program only when it’s actually pressed?” This introduces the concept of an event as a notification—a more efficient way to code.

How does a switch work?

We are going to create an alarm that is activated by a switch. But to do that, we need to understand how a switch thinks. In programming, a simple switch has two possible states:

• On: The switch is activated. We can represent this state with the number 1.
• Off: The switch is deactivated. We can represent this with the number 0. A switch can only be in one state at a time. By reading whether the state is 1 or 0, the computer can decide what to do next.

How does the computer know the state?

The computer can be programmed to “listen” for a signal from the switch. Every time the button’s state changes (from Off to On, or On to Off), it notifies the computer! This notification is called an event. Once the computer receives the event, it can run a specific piece of code to react to it.

Why not just use a main loop?

Using a Main Loop to check a button is like a backseat driver constantly asking: “Are you pressed yet?! How about now?! Are you pressed now?!” even when nothing is happening. It’s repetitive and wastes the computer’s energy. With events, the program is quiet. It just waits. The switch itself sends a single signal to the computer only when its state has changed. This is much more efficient and professional!

We received the event… Now what?

Once the switch sends its signal, the computer can use a conditional to decide what to do based on the switch’s current state. For our alarm, the logic is simple: IF the switch’s new state is ON, we play a sound. ELSE (meaning its new state is OFF), we stop the sound.

Development (20-30 minutes) - Building an Event-Driven Alarm

1. Now that the students understand the difference between constantly checking with a loop and efficiently listening for an event, it’s time to build the smarter alarm.
2. Lead them through the instructions for building the event-driven program, as detailed in the hands-on section below. Emphasize that this program’s main logic does not use a “repeat forever” loop, because the event does the work for us.

Closure (5-10 minutes) - Events are Everywhere

1. Once everyone has a working, event-driven alarm, it’s time to reflect on this powerful new programming paradigm.
2. Use the final section to spark a discussion on where else events are used in modern technology (every click, tap, and notification is an event!) and to challenge them to combine events with variables to add a new feature.

Reflect

You’ve just learned a more professional way to code!

Events are the backbone of all modern user interfaces—every click, tap, and swipe is an event. Besides buttons, what other things on your phone or in a game could trigger an event? (Think about notifications, finishing a download, a character touching a coin, etc.)