WhatsApp is testing out a new Record voice message feature that will allow its users to leave voice notes in case of missed voice calls. The feature made an appearance in the latest WhatsApp beta build 2.25.23.21 for Android.
Spotted by WABetaInfo, the feature is currently being rolled out to WhatsApp Beta for Android users via the Google Play Store. This new feature is part of the notifications reminders feature for missed calls, which went live with the WhatsApp beta 2.25.22.5 build for Android a while back.

As it is evident from the above image, users can now record a voice message when the recipient fails to answer a WhatsApp call. The Record voice message option will be displayed within the recipient's chat window as an extended option within the missed voice call chat bubble.
This is a handy feature since it will allow users to reach through in case of urgency. Users will not have to wait for another time to call. They will be able to simply leave a short voice note that the recipient can come back later to.
It is essential to note that this feature is distinct from the existing voice message interface, which has been in place for a long time. Users will still be able to leave normal voice messages and in terms of functionality, it is not that different.
This feature works in tandem with the existing missed call reminder, and the recipient will be able to view both the missed call notification and the voice message one. That said, some WhatsApp beta testers on Android are already able to make use of this new voice message feature. We can expect it to make its way to iOS TestFlight soon, with a wider rollout thereafter.