My four-year-old British Blue cat Sheila was the very definition of aristocratic calm.

About two months ago, her behaviour changed radically and, honestly, quite frighteningly. Every night, as soon as the evening noise died down and I sat in the living room with my book, Sheila would suddenly jump up, arch her back and stare with wide, terrified pupils into the left corner of the room. There was nothing there, just an empty bookcase and an old standing lamp. But she started attacking the empty air right next to the wall, very aggressively. While doing it she made these low, throaty sounds that gave me goosebumps.

I was starting to go crazy. My mother insisted that animals can see ghosts and there must be some kind of negative zone inside that wall. I tried distracting Sheila with treats, even picking her up, but at that moment she was completely out of it – hissing at me and refusing to take her eyes away from that empty corner. The strangest thing was, that as soon as I turned off the lights and went to bed, the attacks stopped immediately.

Last week my brother came to visit me. He works installing security systems and smart home networks. When he saw Sheila's nightly madness, he didn't start talking about cat schizophrenia or paranormal things. Instead, he took out his toolbox and started checking all the electronics in the room systematically.

He took out a thermal camera and a specialised acoustic analyser, the kind which is used for measuring structural vibrations in buildings. As soon as he put the device against that “empty” wall, the mystery was solved almost immediately.

Directly behind that wall, in the hallway of the house, there is the main electrical breaker box and a new digital electricity meter, which the energy company installed at the beginning of summer. My brother discovered that one of the internal components inside the box had a microscopic manufacturing defect. Every evening around ten, when the electricity company sent a signal to switch to the night-time tariff and I turned on the old standing lamp in the living room, the change in electrical load was enough to make the faulty coil inside the box fall into a strong mechanical resonance.

This physical effect started producing intense, pulsing ultrasound and microscopic vibrations. The living room wall acted like a huge soundboard, transferring those invisible vibrations directly into the room.

To the human ear it was complete silence. For me, sitting in the living room, the house seemed perfectly quiet. But for a cat's extremely sensitive hearing and her whiskers, it was an unbearable, scratching roar. The sound was also bouncing around the enclosed corner and reflecting from the walls. Sheila wasn't fighting ghosts and she hadn't gone crazy. Because she couldn't locate the source of the invisible noise precisely, she attacked the empty air, simply trying to get rid of an enemy which was brutally disturbing her territory every single night.

The next day I called the emergency repair line and had the breaker and electricity meter replaced. Today Sheila is happily snoring in her armchair again, and I finally know that the house is completely quiet.

(please excuse my english, it's not my native language but i just had to share this crazy current event with you guys)

Sources

• Merck Veterinary Manual – Ear Structure and Function in Cats: Cats are highly sensitive to sound and can hear a much wider range of frequencies than humans. Their ears can also move independently, helping them identify the direction from which a sound is coming. This makes unusual high-frequency sounds that are completely inaudible to humans potentially significant to a cat.

• VCA Animal Hospitals – Why Do Cats Have Whiskers?: A cat's whiskers are highly sensitive sensory structures. Their follicles contain numerous nerves and blood vessels, allowing cats to detect subtle changes in air movement and vibrations around them. This sensory system helps cats navigate their surroundings and detect nearby objects even in low light.

• Merck Veterinary Manual – Physical Description of Cats: Cats possess considerably more sensitive hearing than humans and use their ears to locate sounds precisely. Their ability to detect and identify sounds is particularly important for hunting and for understanding what is happening in their immediate environment.

• VCA Animal Hospitals – Functions of Cat Whiskers: Whiskers can detect very small movements and changes in air currents. The information gathered by these specialized hairs is transmitted through sensory cells to the cat's brain, effectively giving the animal an additional way of detecting movement and objects nearby.

• Schneider Electric – Energy Meters Technical Documentation: Modern electricity meters can operate with multiple tariff systems. Depending on the installation, tariff changes may be controlled through communication signals, digital inputs or an internal clock. This provides technical background for the possibility of electrical equipment changing its operating state at a predetermined time.

• Merck Veterinary Manual – Deafness in Animals: Veterinary literature notes that cats can detect frequencies well above the range normally perceived by humans. High-frequency hearing is particularly important in cats, and changes in their ability to hear such frequencies may not be obvious to their owners.