My Philips Avent Baby Monitor beeps

Baby unit is turned off: When the baby unit is turned off, the parent unit will beep once and show the out-of-range image on its display. Make sure that the baby unit is turned on.
The connection between the units is lost: If the connection between the units is lost, the link light turns red. The parent unit beeps three times every 20 seconds, and the out-of-range image appears on the display. Try a different location or decrease the distance between the baby unit and the parent unit. It can take up to 10 seconds before the connection between the units is reestablished.
Battery of the parent unit is running low: If the battery of the parent unit runs low, the parent unit beeps every 20 seconds. Recharge the battery of the parent unit. When you charge the parent unit for three hours, it can be used cordlessly for approx. 10 hours.
Maximum or minimum temperature is reached: Note: This situation is applicable to the following models of Philips Avent Baby Monitor: SCD630, SCD831, SCD833, SCD835, SCD841, SCD843, SCD845, SCD881, SCD882, SCD891, SCD892.
The parent unit will beep twice every 20 seconds when the baby unit reaches the chosen maximum or minimum temperature. The parent unit shows a temperature that is exceeded. Go to temperature settings to change the maximum and minimum temperature or to turn off the temperature alert. If this is not solving the issue, please contact us for further assistance.

Baby unit is turned off