skvallerspegel

skvaller (“gossip”) +‎ spegel (“mirror”), used since 1897. In Danish called gadespejl (“street mirror”).

skvallerspegel c

1. a double mirror mounted outside a window, for viewing up and down the street; similar to a rear-view mirror, but mounted on a house; common in small towns with wooden houses (Kalmar, Vadstena)
   • Hjalmar Bergman, 1919, Markurells i Wadköping, chapter 5

     Och där satt hon, till synes bunden av sin vana och sin kära skvallerspegel, som fängslat henne i ett drygt halvsekel.

     And there she sat, apparently spellbound by her habit and her dear mirror outside the window, that had held her captive for more than half a century.

• espion[1][2]
• reflexionsspegel

• skvallerspegel in Svenska Akademiens ordlista över svenska språket (13th ed., online)
• skvallerspegel in Svenska Akademiens ordbok online.