The 30-year-old has penned a 12-month contract with the Bundesliga club, where he will provide back-up to number one Ron-Robert Zieler.
He may stand in goal when Hannover start the season since Zieler is not expected back in training until early August.
"We are reacting to our goalkeeper situation and are delighted to have managed to get such an experienced custodian," said Hannover's director of sport Dirk Dufner.
"Robert Almer will join us in training from Monday and that's a big help since our number one Ron-Robert Zieler is not going to start training for another week after his post-World Cup holiday."
Hannover's first serious test of the new season comes in the first round of the DFB-Pokal, when they travel to fourth-division side Astoria Walldorf on 16 August.
A week later, they get their Bundesliga campaign under way with a home game against Schalke.