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What a kill switch can and can't do for a manual trader

A kill switch is the tool we're asked about most. It helps, but it isn't magic. Here is exactly what it can and can't do.

Last reviewed November 2026

What it can do

• Watch your rules all day. Daily loss limit, profit lock, a cap on trades, a time cut-off, and locked days such as the day before expiry, checked against the broker about once a second.
• Close everything when a rule breaks. Cancel pending orders and stops, exit open positions at market, and confirm each exit filled.
• Keep you out for the rest of the day. If you open a new position after the trip, it is closed again within a second or two.
• Lock the account at the broker. Some brokers offer their own kill switch through the API. On Upstox the software can turn it on after a trip, so the broker itself refuses new orders. Once on, Upstox keeps it on for about 12 hours.
• Put a stop on every trade. A stop-loss on each manual trade within seconds, so a forgotten stop can't become a big loss.

What it can't do

• Stop the broker accepting your order. Unless the broker's own lock is on, the order goes through first and the software reacts after, usually within one to two seconds. Prices can move in that time.
• Lock every broker. Not every broker has a kill switch you can reach through the API. Zerodha's Kite Connect has none, so there the software can only close and re-close.
• See an account it can't read. If your login expires or the broker's API is down, it can't check your P&L. A good one tells you straight away rather than assume all is fine.
• Make a strategy work. It limits how much a bad day can cost. It doesn't make anything profitable.

Questions to ask before you rely on one

• Does it read P&L from the broker, or work it out itself? Working it out can go wrong on short positions and charges.
• Does it count trades from the broker's trade book, or trust its own counter?
• What happens if it can't read your account?
• What restarts it if it hangs?
• Can you turn it off in the middle of a bad day? A good one doesn't let you.

Our own kill switch is described in the kill switch case study.

General information from building and running these systems, not legal or investment advice. Brokers change their APIs and rules; check your broker's current documentation before relying on any detail here.