The pacy winger, 23, arrives at the Hawks having failed to feature in any of the Spitfires' past three National League matches.
Horndean-based Smart, who has made 94 appearances and scored five times since his move to Eastleigh in the summer of 2019 from Basingstoke Town, has now sealed a short-term switch to Westleigh Park as he searches for more regular minutes between now and the end of the season.
And boss Paul Doswell believes Smart will bring a much-needed injection of pace into his squad following the departure of Abdulai Baggie last month.
‘He's someone we've known for two years, he lives in Horndean with Benny Read, Sam was very keen to come in and we were keen to get him,’ said Doswell.
‘We were looking for that pacy wide player, ever since Baggie (Abdulai) left the club, that's what we've been looking for.
‘I think we bided our time well and brought in a player who's going to improve us with pace in those wide areas.
‘From Sam's perspective, he hasn't played enough games in the past seven or eight weeks and it's an opportunity for him to come to this football club and play football. That's where it came from, really.’
Smart made 32 appearances and scored 12 goals during a spell with hometown club Horndean under Michael Birmingham in the Wessex League Premier between 2015-17.
After a move to Basingtoke Town followed, the former Horndean Technology College pupil had spells on trial with both Sunderland and Sheffield Wednesday but failed to earn a professional deal.
This season Smart has been restricted to 15 outings for Eastleigh and has failed to score. He joins former Horndean team-mate Benny Read in the Hawks squad and is in contention to make his debut in Doswell's side's trip to Concord Rangers.
The Hawks will be desperate he can inspire a turnaround in their fortune having now gone eight National League South matches without a victory.
Smart becomes Doswell’s fourth addition of what is proving a busy month following on from the arrivals of Stefan Payne and Alfy Whittingham – on loan from Chesterfield and Aldershot respectively – as well as striker Manny Duku.