Small bodies mean trade-offs
A smaller camera holds a smaller battery. Mini cameras are excellent in motion-triggered standby, where they can wait for days or weeks and record only when something happens, but continuous recording drains them quickly. If you need constant recording, either choose a model that can stay plugged in, or look at a mains-powered hidden camera built into a charger or clock instead.
WiFi models let you watch live and get motion alerts on your phone. Where there is no WiFi, such as a shed, a gate or a bach, a 4G model with a SIM slot is the only option that reaches you.
Related
To build a camera into something yourself, see DIY spy cameras. To carry one instead of placing it, see wearable spy cameras.
Common questions
How long does the battery last? Hours in continuous recording, days or weeks in motion-triggered standby.
Can it record in the dark? Most have infrared night vision, which records in full darkness without a visible light.