What the Impinj M800 generation changes about tag selection
What a newer UHF chip buys you in practice: the same read performance from a smaller tag, and fewer dead spots on difficult surfaces.
Two things decide how an RFID tag performs: the antenna design and the chip inside it. The tag manufacturer designs the antenna. The chip comes from one of a handful of silicon vendors, and Impinj is the most widely used of them. M800 is their current generation.
Why sensitivity matters more than range figures
Read sensitivity tells you how little energy the tag needs in order to wake up. It is quoted in dBm and it is negative. The lower the number, the less signal the tag needs.
On site that shows up three ways. You read from further away at the same reader power. You fit the same read distance into a smaller antenna, which means a smaller tag. Or you lose fewer reads in the awkward positions where signal is already weak, at the back of a shelf or inside a packed carton.
The third one matters most. In a stocktake the problem is rarely average read distance. It is the few percent that never read at all, and that is what forces a second pass.
A smaller die buys design room
The other practical gain in this generation is physical: the chip is smaller, which gives the tag designer room to work. In jewellery a tag has to fit inside a ring label. In textiles it has to survive inside a narrow sewn band. In electronics it sits on a small card. Space is always tight.
We see the difference clearly in the industrial tags we manufacture. On-metal tags already work under a constrained antenna design, so a chip that wakes on less energy makes that constraint easier to live with.
Read the datasheet for the model, not the family
M800 is a series, not a single part. User memory, EPC field length and sensitivity vary between models. If you know how long your serial numbers need to be, you already know which model is enough.
Take exact figures from the manufacturer current datasheet. Most comparison tables were measured with a specific test antenna in a specific environment, and they will not reproduce exactly on your floor.
A better chip does not fix a bad install
If you have a read problem, the chip is not the first place to look. The surface the tag sits on, the angle of the reader antenna, the power setting and how tightly tags are packed together usually matter more. A good tag on the wrong surface performs worse than an ordinary tag on the right one.
Put a newer chip on top of a correctly built system and you gain. Use it to paper over an installation mistake and you have spent money without solving anything.