The 30 year-old striker scored two goals fir the Shrimpers with his second coming after Phil Brown's side were reduced to 10 men with Gary Deegan being sent off in the 51st minute.
The former Peterborough United forward netted again from the penalty spot in the 68th minute after Will Atkinson was fouled inside the box by Coventry keeper Reice Charles-Cook to give Southend a gritty victory over Tony Mowbray's Sky Blues who fell to fifth on the League One table.
Barnett was thrilled to contribute heavily to a much-needed and morale-boosting victory for his loan club.
“As a striker, there's no better feeling than scoring goals," he told the club's official website.
“So I'm very happy to score two, but I'm always happier to get the three points, because that's what really matters come the end of the season."
Barnett's influential performance against Coventry proved he is a huge asset in their playoff push. His second goal underlined his impact and importance, with his team going a man down, he popped up when needed to coolly finish the tie by firing into the roof of the net from 12 yards.
If the Essex outfit are going to find themselves in the promotion playoffs come the end of the season, and repeat last season's promotion from League Two, Barnett will be crucial as he has already shown with three goals in three outings since crossing from league rivals Shrewsbury for the remainder of the season.
BARNETT | "A lot of teams always seem to get back to back promotions and why can't this happen? We've got a great squad & management."
— Southend United (@SUFCRootsHall) January 23, 2016
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By Joe Baker