I like to use the lift test.
The next step in determining picking readiness is ease of fruit removal. If you notice several pears dropping from the tree, you may be too late, but it's a sure sign they should all be picked. Every few days as you approach the harvest period above, give the pears the "lift test." Putting your index finger on the stem, lift the pear from the normal vertical orientation to a horizontal or flat position, perhaps with a slight twist. If the fruit "snaps" off cleanly between the stem and the twig, the pears are ready to strip from the tree. If you have to wrench off the fruit either breaking the twig or the fruit stem, the fruit is probably not ready. On larger trees, fruit growing in the top often ripens earlier than fruit in the shaded interior.