Two ways to use a spy camera
The first question is whether the camera stays put or comes with you. If you are watching a room while you are elsewhere, a hidden camera built into a clock, charger or speaker sits in plain sight and records continuously. If you need footage while you are moving, a wearable camera in a pen, glasses or a watch travels with you.
The second question is power and connection. Battery models go anywhere but need recharging. Mains-powered ones, especially chargers and clocks, run for as long as they stay plugged in. WiFi models let you watch live from your phone; if there is no WiFi where the camera goes, look for a 4G model with a SIM slot.
Where to start
Browse hidden cameras for disguised units, mini spy cameras for the smallest bodies, nanny cameras for indoor monitoring, or DIY spy cameras if you want to build a camera into something yourself.
How long they actually record
This is where most disappointment comes from. A battery-powered covert camera recording continuously runs for one to three hours, because the device is the size of a matchbox and the battery is the size of a stamp. That is fine for a meeting and useless for a week.
Motion detection changes that: it means the camera sleeps until something moves, which turns a two-hour battery into several days in a quiet room. Mains power removes the limit altogether, which is why the objects that already live plugged in, chargers, clocks, speakers and smoke alarms, are the practical choice for anything long term.
Card capacity, and what it means in hours
At 1080p, an hour of video is roughly 1GB. At 4K it is closer to 4GB. A 128GB card therefore holds somewhere around five days of continuous 1080p footage, or a great deal more if the camera only records on motion. Most units loop, overwriting the oldest file when the card fills, so the question is not whether it runs out but how far back you can still go.
What gives a camera away
An indicator light, which is why the better units either have none or let you disable it. Heat, because a device recording continuously in a sealed plastic case gets noticeably warm to the hand. And placement, which is the one nobody thinks about: an object that has moved, or that has appeared, or that is pointed somewhere odd, is what people notice long before they notice a lens.
If you are on the other side of this and want to check a room rather than watch one, see spy camera detectors.
Common questions
Do spy cameras record sound? Many do. Audio recording carries different rules from video in New Zealand, so check what applies to your situation before you record conversations.
Do I need WiFi? Only for live viewing. Offline models record to a memory card and you review the footage afterwards.
How long do they record? Battery models typically run several hours of continuous recording, or weeks in motion-triggered standby. Mains-powered models run without limit.