The Philips Avent Videophone SCD921/26 is identical in construction to the Philips Avent Videophone SCD923/26, which is also available. The different designation results from the fact that the Philips Avent Videophone with the designation SCD921/26 is only sold through specialist retailers.

According to the official Philips homepage :

Philips Avent Connected Videophone SCD923/26

Secure Connect System for a secure connection between baby and parent unit and Baby Monitor+ app (iOS/Android)
Baby unit with full HD camera including zoom and night vision function
Integrated ambient night light
15 sleep sounds and lullabies
Rechargeable parent unit with up to 12 hours of battery life
4.3 inch colour display
With real conversation function for simultaneous listening and speaking
Range between units: 50 metres indoors and up to 400 metres outdoors
Room thermometer including high and low temperature alarm
"Try&Buy": Test the Videophone before you buy
Colour: Grey
Recommended retail price (RRP): 299.99 euros
Available from September in the Philips online shop


Philips Avent Video Baby Monitor SCD921/26:
Same as SCD923/26, except:

Colour: Beige
Recommended retail price (RRP): 299.99 euros

I had asked myself the same question.
Answer: Radio 2.4 GHz & WLAN (app connectivity from everywhere) !

The charging socket is much better and the charging cable more stable! Battery lasts longer overall the quality is better than the predecessor ! I am very satisfied !

According to the manufacturer, the products are technically identical (https://www.philips.de/a-w......). The specifications are also 1:1 identical (https://www.philips.ch/c-p... resp. https://www.philips.ch/c-p...).