What ready actually looks like, stage by stage
A staged introduction earns the whole house in layers, and each layer leaves evidence you can check. Behind a closed door, ready cats eat their meals close to the door without pausing to stare, growl or abandon the bowl. During scent swapping, each cat sniffs the other's bedding or a rubbed cloth and then rubs, rests or simply moves on, rather than hissing at the smell or avoiding the spot for hours. On site swaps, each cat explores the other's room, uses the tray, eats a treat and settles, instead of pacing the door line or scent-marking in agitation.
Through a screen, gate or cracked door, the clearest sign is boredom. Ready cats glance at each other, blink slowly, turn sideways, groom, or wander off to a perch. Ears stay in their normal position, tails move loosely, and neither cat crouches low with a fixed stare, puffed tail or repeated lunging at the barrier. If one cat retreats, the other lets her go. That ability to disengage matters more than any brief nose touch.
Test short shared sessions before open access
When the barrier signs have been calm for several consecutive days, start brief meetings in the largest, most escape-rich room, with treats and play happening at opposite ends. Keep the first sessions to a few minutes and end them while things are still easy, guiding each cat back to her own area with food rather than picking her up mid-tension. Gradually lengthen the sessions and add the ordinary moments that test tolerance: one cat crossing to the water bowl, the other using a scratching post nearby, both hearing a normal household noise without blaming each other for it.
Provide duplicates before you provide freedom. Two feeding areas, at least one tray per cat plus a spare in different locations, separate resting heights and two routes out of every shared room prevent the quiet resource pressure that turns a promising introduction sour a week later. A cat who can always leave does not need to fight to stay.
Signs to step back a stage, not push through
Hissing once during a surprise face-to-face moment, then both cats retreating and recovering within minutes, is information rather than failure. Go back a stage when you see a pattern instead: one cat repeatedly waiting outside the other's door to ambush, guarding trays or food, staring without breaking off, or chasing that ends with the other cat hiding and skipping meals. Also step back if either cat stops eating, over-grooms or starts toileting outside the tray after sessions begin — stress often shows in the routine before it shows in a fight.
Stepping back means returning to the last setup that produced calm behaviour for several days, not restarting from day one. Patience at this point is what protects the relationship; forcing shared space on two cats who are merely tolerating the barrier usually creates the very conflict the slow introduction was designed to avoid.
Open the house one boundary at a time
Even after good shared sessions, expand territory gradually: open one additional room for part of the day, keep night-time separation a little longer, and only leave them unsupervised together once you have seen relaxed coexistence across different times, rooms and energy levels, including the dawn active hour. Keep each cat's original safe room available permanently as a retreat, not as a prize that full access removes.
Sharing the profile of each cat through KinsLe Family Sharing with the relatives you choose means a family member opening the app meets the two individuals whose introduction this is, rather than a generic pair of cats.