Barbara and Adam Maitland decide to spend their vacation decorating their idyllic Connecticut country home. As the two are driving home from a trip to town, Barbara swerves to avoid a dog and the car plunges into a river. After they return home, she and Adam notice that they now lack reflections and they discover a Handbook for the Recently Deceased. They then begin to suspect that they did not survive the car accident; Adam attempts to leave the house but finds himself in a strange, otherworldly landscape covered in sand and populated by enormous sandworms.
The house is sold and the new owners, the Deetz family, arrive from New York City. Charles Deetz is a former real estate developer; his second wife Delia is a self-proclaimed sculptor; and his goth daughter Lydia, from his first marriage, is an aspiring photographer. Under the guidance of interior designer Otho, the Deetzes transform the house into tasteless pastel-toned modern art. Consulting the Handbook, the Maitlands travel to an otherworldly waiting room populated by other distressed souls, where they discover that the afterlife is structured according to a complex bureaucracy involving vouchers and caseworkers. The Maitlands' own caseworker, Juno, informs them that they must remain in the house for 125 years. If they want the Deetzes out of the house, it is up to them to scare them away. Barbara's and Adam's attempts at scaring the family prove ineffective.
Although Adam and Barbara remain invisible to Charles and Delia, teenage Lydia can see the ghost couple and befriends them. Against Juno's advice, the Maitlands contact the miscreant Beetlejuice, Juno's former assistant and now freelance "bio-exorcist" ghost, to scare away the Deetzes. However, Beetlejuice quickly offends the Maitlands with his crude and morbid demeanor; and they reconsider hiring him, though too late to stop him from wreaking havoc on the Deetzes. The small town's charm and the supernatural events inspire Charles to pitch his boss Maxie Dean on transforming the town into a tourist hot spot, but Maxie wants proof of the ghosts. Using the Handbook for the Recently Deceased, Otho conducts what he thinks is a sĂŠance and summons Adam and Barbara, but they begin to decay and die, as Otho had unwittingly performed an exorcism instead. Horrified, Lydia summons Beetlejuice for help; but he agrees to help her only on the condition that she marry him, enabling him to freely cause chaos in the mortal world. Beetlejuice saves the Maitlands and disposes of Maxie, his wife, and Otho, then prepares a wedding before a ghastly minister. The Maitlands intervene before the ceremony is completed, with Barbara riding a sandworm through the house to devour Beetlejuice.
Finally, the Deetzes and Maitlands agree to live in harmony within the house. Beetlejuice , meanwhile, is stuck in the after-life waiting room; there he antagonizes a witch doctor, who shrinks his head. Being Beetlejuice, however, he remains upbeat: "This could be a good look for me."

Question: How do Adam and Barbara find out they are dead?
Answer: They find The Handbook for the Recently Deceased.
Alternative answer: They lack reflections and have a guidebook on being dead.