I have another surprising piece of information for you, at least I would not have expected it today. In some countries the new Philips Hue Secure Contact Sensor is already listed in the Hue online shop and can be ordered there. Unfortunately, I don't have complete information on which countries the sensor is available in.
Hue Secure contact sensor available in first countries New accessories for Philips Hue
New accessories for Philips Hue