Does the pattern day trader rule affect automated strategies?

Only if a strategy round-trips the same ticker within a single day, four or more times in five business days, in a margin account under $25,000 — that's what flags a pattern day trader (PDT) and restricts further day trades. Most systematic retail strategies are structurally safe: a Monday entry with a Thursday exit is not a day trade, and neither is a profit target that fills the day after entry. The templates most likely to brush the rule are fast mean-reverters on volatile tickers, where an entry and its target can fill the same session. Mitigations: cash accounts (no PDT rule, but settlement timing applies), slower exits, or simply awareness — check your strategy's backtest for same-day round trips before deploying it small.