Petsafe deluxe ultralight Guide D'emploi page 11

The Receiver Collar is equipped to automatically increase the level of
Static Correction the longer your pet remains in the Static Correction
Zone if the collar is set at level 2 or above.
The Receiver LED Indicator Light acts as a low battery indicator, flashing
every 4 to 5 seconds when replacement is required.
Over Correction Protection
In the unlikely event that your pet "freezes" in the Static Correction
Zone, this feature limits the static correction duration to a maximum of
30 seconds. While the system locks out further static correction, the
warning tone will continue until the pet leaves the Static Correction
Zone.
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