Signal
Information the program can read.
Topic Guide
Sensing and Collision
Sensing blocks report contact, colour, distance, button presses, and other changes a program can use.
Why this matters
A moving sprite needs to notice walls, hazards, and targets. A robot needs a reading from outside its command list before it can respond to a box placed in its path.
Beyond this topic
A door sensor may use a physical switch; a game uses the shapes of two costumes. In both cases, the designer has to define exactly what counts as contact.
Math and logic
Collision
Two defined areas touch or overlap.
Boundary
A position or region where the rules change.
Continuous checking
A loop reads changing input again and again.
Small examples
Touching colour
Use a map colour to mark a wall or hazard.
Sprite collision
Check whether the player and target overlap.
Distance reading
Respond when an obstacle is nearer than a set limit.
Button sensing
Read whether a physical control is pressed.
Program connections
Where this topic appears.
Active now
Scratch & Game Design
Students author games, animations, simulations, and strange interactive stories while learning how events, rules, and state fit together.
Active now
Robotics
Students write commands, wire simple circuits, read sensors, and trace physical cause and effect through the Sense–Decide–Act loop.
Coming later
Roblox Studio / Lua
A possible later step from visual programming into Lua, 3D objects, events, and larger game rules.
Common mistakes
Surprising collision area
A costume is larger than it looks, so contact happens too early.
One-time check
The player moves after the collision test has already finished.
Repeated scoring
One long contact adds a point on every trip through the loop.
Trusting the picture
The sprites look close, but the sensing block reports something else.
Put the idea to work
Scratch & Game Design
Guided Project
The Floor Is Definitely Lava
Build a one-room platform game with a controlled jump, safe platforms, lava, and a clean restart.
See how it works
Scratch & Game Design
Computer Lab Project
Astro-Chicken Rescue
Track several drifting chickens, collect them once each, and stay out of the danger zones.
See how it works
Robotics
Guided Project
Button and Buzzer Alarm
Connect a button to a visible and audible alarm, then write clear rules for arming, triggering, and resetting it.
See how it works