The phrase "alert online" is correct and usable in written English.
It can be used to indicate that someone is currently active or available on an online platform, often in the context of messaging or social media.
Example: "I noticed that she is alert online, so I decided to send her a message."
Alternatives: "active online" or "available online".
The system will monitor data from 50,000 Web sites with many types of information, including World Health Organization alerts, online discussions by experts, wildlife trade reports and local news.
The movies and TV shows are just one feature in a landscape of viral marketing campaigns, merchandising tie-ins, spoiler alerts, online chat forums, fan blogs, websites that treat fictional worlds as real places, and so on.
The Web site's declaration of a Bush triumph was echoed in an e-mail message that The Times on the Web sent to users who have registered for such alerts online; the e-mails, like newspapers already deposited on doorsteps, could not be recalled.
Amazon Wine's customer base will also be notified via email, and a message will display on the Amazon Wine homepage alerting online shoppers to the closing.
Recent enhancements include listings for river cruise lines, cruise price alerts, online booking and itinerary maps.
Since MHRA started reporting drug alerts online in 2001, there has been a gradual increase in the rate of drug alerts related to defective medicinal products.
Just came across your website (from a Google Alert on 'Online Dispute Resolution').
Ricky Ashenfelter, MBA '15, co-founded Spoiler Alert, an online platform to help businesses manage food donations and reduce food waste.
Meanwhile, British security services are reported to be on "high alert" after online "chatter" emerged from jihadists discussing plans to murder soldiers, police and intelligence operatives in the UK.
Mr. Khosrowshahi said the company did not break out taxes and fees on hotel rooms because doing so would alert other online booking services to deals that Hotels.com or Expedia have made with lodging chains.
