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Planner Cameras Doorbells Locks Answers How we calculate

How we calculate

The planner uses manufacturer specs, not lab tests. It works out how far each camera can usefully see from its resolution and lens angle. It checks what the house blocks on a 2-foot grid, then prices hardware plus the cheapest plan that lets each device record. Every threshold is on this page.

1. How far a camera can usefully see

Security designers measure detail in pixels per foot (px/ft) at the target. We use three levels: detect at 8 px/ft (something is there), recognize at 20 px/ft (a person you know, a car's color and shape), and identify at 40 px/ft (a stranger's face). The planner's range for each camera is the recognize distance:

range = (sensor width px ÷ 2 ÷ tan(field of view ÷ 2)) ÷ 20

  • Example: a 2K camera (2560 px wide) with a 140° lens recognizes out to about 23 ft.
  • Lenses wider than 150° are calculated as 150°. Ultra-wide lenses are distorted, and the simple formula would otherwise overstate their range.
  • When a brand publishes only "2K" or "4K" rather than pixel counts, we use the lowest common width for that label (2K = 2304 px, 4K = 3840 px) and mark it as assumed.
  • Range is capped at 60 ft, and at the published motion-detection range when there is one. Battery and solar cameras only record when their motion sensor fires, so without a published figure we cap them at 40 ft, which is typical for PIR sensors.

2. Night vision

  • We use the published night-vision distance when there is one.
  • Floodlight cameras (700 lumens or more) light the scene, so we allow at least 40 ft at night, never more than the daytime range.
  • With no published figure we assume 30 ft for infrared, 30 ft for spotlight color night vision and 25 ft for low-light color sensors, and label it as assumed.
  • Areas you mark as lit at night use the daytime range.

3. Blind spots

Each area in a layout is split into 2 × 2 ft cells. A cell counts as seen when it is inside a camera's lens angle, within its range, and the straight line from the camera to the cell doesn't pass through the house, garage or another building.

A required area is a blind spot when less than 70% of it is seen, or when no camera sees one of its key spots (the front step, the garage door, a gate). At night, an area is flagged when its seen share drops below 60% of the daytime figure or a key spot goes dark.

4. How the planner places cameras

Layouts come with realistic mounting points: eaves, porch lights, outlets and the door frame. For each goal the planner adds one camera at a time. It tries every free mount, direction (15° steps) and eligible model, and keeps the one that helps most, until the required areas are covered and the next camera adds little. It never uses more than 8 cameras.

  • Lowest 3-year cost: the most coverage per dollar of hardware plus 36 months of plan fees.
  • Easiest install: no new wiring, and one brand where possible, so one app.
  • Most coverage: the most area seen by day and night within your budget.

If required areas can't be covered, we loosen settings in this order and tell you: budget +20%, then allow monthly plans, then allow wiring. Cameras you already own stay where they are and cost nothing.

5. Power at each spot

  1. Door frame with doorbell wires: wired doorbell. Otherwise a battery doorbell.
  2. If you can run cable: PoE first, then a floodlight on an existing light fixture, then an outlet.
  3. If you won't run cable: an existing light fixture or outlet.
  4. Otherwise solar, unless the spot is in full shade.
  5. Otherwise battery.

6. Battery estimates

Brands state battery life under a usage assumption, such as "300 days at 230 seconds a day". We convert that to your spot's expected motion events per day, assuming 20 seconds of activity per event. When a brand gives only a number of days, we assume the claim was measured at 10 events a day. We never estimate longer than the brand's own claim. In cold climates we multiply by 0.5: lithium cells lose capacity and won't charge below 0 °C (32 °F).

7. Wi-Fi reach

signal (dBm) = −30 − 22 × log10(distance ft ÷ 3.3) − outside walls × 10 dB (wood) or 15 dB (brick, concrete) − inside walls × 4 dB

We count one inside wall per 12 ft of path through the house. At -65 dBm or better the signal is good, down to -75 dBm it is borderline, and below that it is likely too weak. We suggest a mesh node just inside the wall nearest the weak spots.

8. Cost

  • One-time cost is the list price of every device plus anything it requires: a base station, PoE switch or lock bridge. Devices you own cost $0.
  • Monthly cost is the cheapest plan tier that unlocks what each device needs: recording for Ring, Arlo, Blink and Nest, plus anything extra you ask for. For several devices of one brand we compare per-device and unlimited plans.
  • 3-year total = one-time + 36 × monthly.
  • Canadian prices are stored per product, not converted with an exchange rate; the gap ranges from about 1.0× to 1.8×. When we have no Canadian price we show the US price and say so.
  • microSD cards, installation labor and taxes aren't included.

9. Data and updates

10. Limits

This is a planning tool, not a site survey. Real yards have trees, fences, slopes, glare and neighbors' lights. Before you drill, tape the camera up or run it on a long cable and check the live view. Mounting height, tilt and weather also change what a camera sees, and we don't model them.