Websockets have a 10-minute inactivity timer; implementing health checks and sending pings every minute is heavily recommended to keep the websocket connection alive.
Helius-specific extension. Can be lock (default) or write.
lock sends a notification for every account a transaction write-locks, even if the transaction never writes to the account
write only sends notifications when a transaction actually writes to the account, cutting duplicate no-op updates for busy accounts. A write of identical data still counts as a write and is delivered