What Are Circuit Breakers and Sidecars? A Guide to Stock Market “Emergency Trading Halt” Mechanisms
When stock prices move sharply in a short period, the market can be swept up by fear or automated orders. In such moments, the Korea Exchange has mechanisms that temporarily halt trading or restrict certain orders. The main examples are sidecars and circuit breakers. Both are designed to cool the market, but the scope of what they stop is different.
| Section | Key summary |
|---|---|
| Introduction | The main examples are sidecars and circuit breakers |
| A sidecar briefly pauses program trading | It does not stop all trading by ordinary investors |
| A circuit breaker halts the entire market | The higher the stage, the stronger the measure |
| What investors should not misunderstand | Activation of this mechanism does not mean losses are prevented |
| What to do when you see an activation alert | You should also check whether it was triggered in KOSPI or KOSDAQ |
A sidecar briefly pauses program trading
A sidecar is a mechanism that suspends the effect of program trading quotes for 5 minutes when futures prices move significantly. It does not stop all trading by ordinary investors. Its purpose is to briefly pause large waves of automated orders and reduce the market’s tendency to rush in one direction.
A circuit breaker halts the entire market
A circuit breaker is a mechanism that suspends all market trading for a set period when the decline becomes larger. The higher the stage, the stronger the measure. Stages 1 and 2 temporarily halt trading, while Stage 3 can close the market for the day.
| Category | Target | Meaning |
|---|---|---|
| Sidecar | Program trading quotes | Cools overheated automated orders for 5 minutes |
| Circuit breaker Stage 1 | Entire market | Temporarily halts trading during a large decline |
| Circuit breaker Stage 2 | Entire market | Adds another halt during a larger decline |
| Circuit breaker Stage 3 | Entire market | Ends trading for the day |
What investors should not misunderstand
Activation of this mechanism does not mean losses are prevented. Prices may fall further or rebound. Rather, it is closer to a tool that briefly pauses rapid order flow and gives investors time to assess the situation. Instead of buying or selling in a hurry based only on the activation news, it is better to review why you hold the position and how much loss you can tolerate.
What to do when you see an activation alert
When you see an alert that a sidecar or circuit breaker has been activated, you should first check what has stopped instead of immediately pressing the buy or sell button. The meaning differs depending on whether only program trading has stopped or the entire market has stopped. You should also check whether it was triggered in KOSPI or KOSDAQ.
These mechanisms are only a way to buy time to stabilize the market; they are not signals that predict the direction of prices. Rather than selling out of fear or buying aggressively in expectation of a rebound, you should use that time to review why you own your stocks, your cash allocation, and the level of loss you can handle.