The Ovilus is a device that supposedly allows itself to be manipulated by spirits, allowing the spirits to "speak" to people. There is a physical version of the device, as well as (seemingly less reliable) apps; while it appears on different shows (such Paranormal State), it is marketed as an entertainment device to its unreliability. It was created by Bill Chappel. A device with a similar purpose (called a Spirit Box) was created by the ITC.
How it Works
The Ovilus has an embedded database of words. It takes readings from the environment (the temperature, atmospheric pressure, and the electromagnetic field) and 'translates' these readings to a number, which references a specific word. The Ovilus can also operate in a 'phonetic' mode, where it reacts to the environment to create words that are not in the embedded database.
A large number of people are skeptical about this device. It appears to be extremely easy to tamper with (especially in the context of TV shows); furthermore, it does not seem likely that any spirit could easily communicate through it. As UFO Nut says in their post :
"If a spirit wanted to answer your question with a specific word, then the spirit would first have to know how to manipulate the embedded software, then scan through a microchip made of millions of transistors, then be able to see which transistors are turned on in a specific binary sequence for the word they’re looking for, then “of-course” they need to know binary conversion; then track back from the transistors through the software. The spirit would also have to know all the different types software programs that could be used to achieve this. After that, the spirit would have to read the data table which assigned a specific number to the word they want, back track that number through another memory chip with millions of transistors, to see how to manipulate the environment, and get your answer."
It is highly unlikely that a spirit would be able to accomplish this feat. If anything, it is an overpriced random word generator, and not a reliable piece of investigative equipment.