On a used car Expert website it said you only have 30 seconds to start up the car after unlocking it, is this true or false

Nope. After all, you could get in and sit in it for hours reading the paper before driving off if you wished. They probably mean a lot of central locking systems, mine included, will relock the car after 30 seconds if you do not open a door. l can unlock mine, remember I've left something and go back indoors and hear it relock again before l get back to it.

l would need more info. but l would say false l never heard of that.

Colin M has it spot on. Some cars will immobilise after 30 secs too. You just need to double plip them to reset.

this is true..this is to stop the car being stolen if you inadvertently leave it unlocked.it is common practice with most manufacturers.not just renault.

False.
But the Megan will re-lock itself automatically if no doors,boots are opened withing 60 seconds.
Boots and doors also lock automatically at 8 mph.

It was true on the early models, with infra-red central locking.
Locking the car with the remote armed the immobiliser, & unlocking with the remote disarmed the immobiliser for 30 seconds. To disarm it after more than 30 seconds u have to point the remote at the receiver (a little black dome on the roof lining near the rear-view mirror) & lock & unlock the doors.

On later first-generation models the central locking used radio, not infra-red, & the immobiliser was linked to a chip in the key, so using the correct key disarmed the immobiliser.

On the Mégane I l the immobiliser is linked to the keycard, & arms when the keycard is removed from its slot (on standard versions) or is outside the car (for versions with the ''hands-free'' card).