The microSD card in a security camera is the only component in the system with a designed-in death date, and it is usually bought with less thought than the cable. Footage gets written continuously, day and night, for years - a workload no consumer card was built for. When the card dies, the camera keeps working, the app keeps showing live video, and nobody notices until the one event that mattered cannot be played back.
The write-load arithmetic
Continuous recording makes the math simple. A 4-megapixel camera at a realistic 4 Mbps writes about 43 gigabytes per day; 2 Mbps halves it, and night recording with IR can push it back up. At 40 gigabytes a day, a year is roughly 14 terabytes written. A consumer microSD rated for phones and photo sessions is typically specified for tens of gigabytes per year of casual use - orders of magnitude below what the camera asks of it. The card is not failing early; it is failing on schedule for a job it was never rated to do.
High-endurance exists for a reason
Surveillance-grade and high-endurance cards carry a workload rating in terabytes written per year, not just a capacity. The rating comes from the controller: better wear leveling, more robust memory cells, firmware tuned for constant overwrites rather than burst writes. The price gap versus a consumer card is small against what a camera system costs, and the endurance rating turns an unknown death date into a spec line you can plan around. Cards marketed for dashcams and security are the same family; cards marketed for phones are not.
The failure mode is full, not slow
Loop recording overwrites the oldest footage, so the card never fills - until cells wear to the point where write cycles start failing. The symptom is not slow recording; it is gaps in the timeline, then a card the camera no longer mounts, then a card that still reports fine in a laptop while the camera rejects it. Some cameras monitor card health and warn before the cliff; many do not. That is why the swap date belongs on a maintenance calendar rather than in a drawer memory.
Counterfeit and mixed cards make it worse
The second-order problem is supply. Counterfeit cards that report a capacity they do not have are common in exactly the channels bulk buyers use, and a fleet with mixed card origins behaves unpredictably - some units drop footage in week three, others run two years. Buying one brand and one model through a traceable channel costs almost nothing and removes an entire class of mystery failures, which matters more as the fleet grows.
Calendar the swap
The practical discipline is unglamorous. Pick an endurance class with a workload rating at least double your measured write load, so the card outlasts the interval you plan. Set a replacement interval - annually for continuous 24/7 recording at mainstream bitrates is a defensible default - and pair the swap with a firmware check so the visit is not wasted. After each swap, trigger a test event and play it back; a card that mounts is not a card that records. If you are specifying security cameras for a fleet, ask our camera manufacturing team which card class the recorder firmware was validated with - start at the factory overview or raise it on the contact page.
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