The best way to tell whether a message has been read is to log onto Facebook with a web browser (or access the Facebook Messenger website by going to messenger.com instead of facebook.com). Clicking on the Messenger icon reveals a list of the people you've communicated with. Selecting a person pop-ups a small window over your Facebook timeline.
Facebook has recently added a read-receipts feature to its events feature in order to attract more users to the feature. A read receipt is a tag that shows whether someone has viewed or seen something. For Facebook events, read receipts will show whether invited guests have viewed the event. This will definitely change the dynamics with which Facebook users viewed the event feature in the past. Facebook most likely added this feature to resolve the problem of people ignoring event invites or trying to appear as though they have not seen event invites, skewing the estimated number of attendees, a problem that I have also experienced many times as well.
Because the read receipts feature forces a response, people will take the Facebook events feature more seriously because its information is more accurate. For example, if the event shows that 1000 people will attend an event, invited guests will base their decision more off of the number of attendees now than before when there was no read receipts feature because the number more accurately represents the number of attendees.
In Google Messages, open Messages. Tap the three-dot menu (More) > Settings > Chat features. Tap Send read receipts.
Read receipts are enabled by default in Facebook Messenger. If you wish to turn them off at some point, sorry, Charlie. You can't. A sneaky workaround allows you to read messages without producing a read receipt.
To turn off WhatsApp read receipts on an iPhone, open WhatsApp and tap Settings > Account > Privacy > and turn off Read Receipts. On an Android, open WhatsApp, select More (three dots) > Settings > Account > Privacy, and turn off Read Receipts.