Continuity mistake: When Constantine manages to get the mirror through the window he falls on his back. To the right on the screen a chair lies on the floor beside a dresser. A few shots later when it cuts to Constantine getting up we can see the chair has changed position as its back now covers the opening of the dresser.
Factual error: When Angela is watching the security video on her laptop of her sister committing suicide, you can see she's playing it using Quicktime. She rewinds a couple of seconds by clicking on the first button of the video player. Actually, when you click this button, it takes you to the beginning of the video. The second button would have rewound it a short time.
Continuity mistake: When Constantine gives Angela Isabel's name tag, Angela is holding the tag so that half the tag is between her fingers and the rest of the half inside her hand. When it cuts half the tag is still between her fingers but the rest of the half is now outside her fist.
Continuity mistake: When Angela visits Constantine you can see an ash tray and two bottles along with other stuff on Constantine's table. Later, when the demons fly outside Constantine's window, as the camera moves over the table you can see all items has suddenly been removed from the table.