Had 2003 VW Beetle (the irony on it - it was made in Mexico).
20 seconds after the door is unlocked and opened mechanically with the key the alarm fires up.
But if in the meantime I managed to crank the engine (factory immobiliser with fob inside the key) the alarm is disarmed.
Haven't tried on newer (and electronically superior) reasonably high-spec (for a van) 2014 VW Transporter but doubt it will be different than the Beetle.
Thinking about it it might be worth checking if I am compelled by law to have the VIN visible at all times.
If not I am going to obscure it right away, just because I am paranoid.