Monaghan County Council has appealed for the return of the defibrillator at the Monaghan town library.
It was taken from the building at around 1.20pm yesterday but hasn't been returned.
It's not known if the defibrillator was stolen or taken for a genuine reason. However, it would be expected if it was taken for a genuine reason that it would have been returned by now.
The Council has appealed for it to be returned to either the Council Offices on the Glen Road, within working hours, or to Monaghan Garda Station.