This is probably just an inconsistency that has never been explained but maybe it has in some novelization or comment by the writers.
On Children of the Gods, Apophis and a group of Jaffa come through an unprotected stargate and surprise a bunch of soldiers taking one hostage. As they go through, the gate activates and then deactivates and a short fight follows in which the soldiers manage to sound the alarm. At that point we can see the stargate is off.
In the next scene on the gate room the stargate is back on and Apophis, Teal'c and the other Jaffa leave.
We know earth does not posses a DHD and it is doubful they would be using the Tauri dialing system. Is it ever explain how Apophis is able to activate the stargate to go back to Chulak?
