The thief or thieves got in through an insecure door and also stole a quantity of cash.
Katy Wood, an investigator with the Priority Crime Team in Bognor Regis, said: “The ring in particular is of great sentimental value to the owners and is a sad loss to them.
“I would ask anyone who may have seen or heard anything suspicious, or who has other information about this incident or the stolen property, to contact us.”
Police have urged all householders to double check that doors and windows are locked before going out or retiring to bed.
Anyone with information should either email [email protected] or phone 101, quoting serial 411 of 4/4. Alternatively, contact the independent charity Crimestoppers on 0800 555 111.