Milesight VS340 vs VS350 vs VS351: desk, doorway or thermopile?

Short answer: These three answer three different questions and none is an upgrade of another. The VS340 tells you whether one desk or seat is occupied — PIR, detection distance within 1 m — so you fit one per desk. The VS350 and VS351 both count people crossing a doorway bi-directionally: the VS350 uses dual PIR and covers a 3.1 m passage width ceiling-mounted at 3 m, the VS351 uses thermopile sensing (plus radar on the battery version) and covers 3.6 m at the same height. All three are LoRaWAN Class A devices available on EU868 for the UK, so one gateway can serve a mix of them.

Which one do I need — desk, doorway or thermopile?

Choose the VS340 if the question is “is this particular desk being used?” It watches one workstation, not a room: 107° × 107° field, detection distance within 1 m, up to 95% recognition. Interchangeable PIR covers reshape that footprint at 70 cm height for a single desk (1 m × 0.9 m), face-to-face desks (1 m × 1.8 m), a bar table (1.8 m × 0.9 m) or a round table (1.8 m × 1.8 m). It is the cheapest of the three per unit, but a 40-desk floor needs 40 of them.

Choose the VS350 if the question is “how many people went through here?” and the opening is narrow. Dual PIR, bi-directional, ceiling-mounted at 2–3 m for a passage width of 3.1 m, or wall-mounted at 1.2–1.3 m for under 2.3 m. Its case for retail doors, washrooms and corridors is battery life: around 9.7 years at SF7 on EU868, or 5.2 years at SF10, quoted at a 10-minute interval and 1,000 people a day.

Choose the VS351 if the doorway is wider than the VS350 covers, or you want a stated counting accuracy figure. Thermopile plus radar on the battery version, 2–3 m installation height, 3.6 m detection width at 3 m, sensor angle adjustable 0–90°, and a quoted 80–90% accuracy for bi-directional counting. It mounts on the ceiling or lintel; the datasheet lists no wall-mount option.

The VS351 is not a newer VS350

The model numbers invite that reading and the power specs contradict it. Every VS351 accepts 5V/1A over USB-C, and the battery version quotes around 1.7 years on 4 × 9000 mAh cells at a 30-minute interval. The VS350 gets its 9.7 years from two replaceable ER14505 cells. With no power at the door, the extra 0.5 m of width costs several battery swaps over the life of one VS350 install.

Two more corrections. The VS340 is not a people counter — it reports the state of the one desk under it, and its “up to 95%” is a recognition figure for occupancy, not a counting accuracy. And the specs do not let you rank the VS350 against the VS351 on accuracy: the VS351 datasheet states 80–90% for bi-directional counting, the VS350 datasheet publishes no equivalent counting-accuracy figure at all.

Will any of them tell me how many people are in the room right now?

Not directly. The VS340 reports occupancy of a single seat. The VS350 and VS351 count crossings in and out of the line they watch; a room-level headcount has to be worked out from those in and out totals by your platform, and neither datasheet claims the sensor reports it. All three capture no images. Both counters are rated for a best operating temperature of 15–30°C, which matters in an unheated lobby, and all three are IP30 indoor devices.

Milesight VS340 / VS341 Desk & Seat Occupancy Sensor – VS340-868M (PIR)

VS340-868M

£43.39 ex VAT (£52.07 inc. VAT)

View the VS340-868M

Milesight VS350 Passage People Counter

VS350-868M

£74.82 ex VAT (£89.78 inc. VAT)

Detection range (passage width)Ceiling mount: 3.1 m passage width at 3 m height; wall mount: under 2.3 m

View the VS350-868M

Milesight VS351 Thermopile People Counter

VS351-868M

£118.21 – £148.14Price range: £118.21 through £148.14 ex VAT (£141.85 – £177.77 inc. VAT)

Detection width at installation height3.6 m at 3 m installation height (installation height range 2 m ~ 3 m)

View the VS351-868M