The BBC offers two different red button services that you access by pressing the red button on your remote control when on a BBC channel.
Red Button Help receiving TV and radio
What's that red button on the radio for?
How does a remote control work the TV? Culture Online - UCL – University College London
Telecare Services - Personal Alarms for the Elderly - Red Button
HDMI splitter vs. HDMI switch: They actually serve opposite purposes - CNET
Josh Wheeler - Founder - Be Broadcast
Red Button Help receiving TV and radio
BBC - Press Red Blog: Say hello to the new look CBeebies
Vision Plus VP5 Digital Amplifier & Signal Finder 4 Caravan Television & Radio 5029833960546