The 29-year-old had spent three years at Meadow Lane when he joined from Gillingham in 2019, playing 63 times and scoring six goals.
Lacey had come through the ranks at Kenilworth Road, making 51 appearances, netting once, before moving to Yeovil Town in July 2015, spending two years with the Glovers.
Former Aston Villa and Crystal Palace youngster Williams elated to make his full Hatters debut in Carabao Cup
Jones could loan out Muskwe and Mendes Gomes as he admits certain players would have left regardless of cup exit
Jones still keen on pushing for defensive signing ahead of deadline day
Luton boss will make a late decision in the transfer window on whether to loan out Pereira
Hatters were aware of McAtee's shoulder injury before agreeing to sign Grimsby striker
However, he has now gone to Victoria Park and speaking to the Pools’ official website, he said: “I am excited to get started at Hartlepool.
"I spoke to the manager (Paul Hartley) about the way he wants to play and the culture he is building and it was a straightforward decision for me after that.
"I have played here before so I know how great these fans are.
"I can't wait to pull on the blue and white.”
Hartley himself added: “Alex is someone who can bring us composure.
"He's a good leader. He can help us build the play out.
"He’s got real quality on the ball and will be a good asset to us.”
Meanwhile, former Luton midfielder Jorge Grant has joined Scottish Premier League side Hearts from Peterborough United for an undisclosed fee.
The 27-year-old headed to Kenilworth Road on loan from Nottingham Forest in July 2018, playing 22 times and scoring four goals, before switching to Mansfield Town.
He then went to Lincoln City for two years, signing for the Posh in June 2021, making 29 appearances and scoring twice, as speaking to the Jam Tarts official website, with manager Robbie Neilson saying: “I’m really pleased to get Jorge in as we continue to build our squad for a historic season.
“He’s an experienced player who will bring dynamism and guile in the final third of the pitch and I’m really looking forward to working with him.
“The squad is starting to take shape but we’re not finished yet and I hope that in the weeks ahead we can continue to add quality to it.”