     // not found, add it if there's still room
     if (unique_num < MAX_MAC) {
         memcpy(&unique_mac[unique_num], mac, 6);
+        unique_mac[unique_num].last_seen = now;
         unique_num++;
         return true;
     } else {

    }
}

// prints a mac address
static void print_mac(const uint8_t * mac)
{
    char text[32];
    sprintf(text, "%02X:%02X:%02X:%02X:%02X:%02X",
            mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
    Serial.println(text);
}

// callback for promiscuous mode


        // check for packet with FromDS=0, packets from station
        if (((fc >> 9) & 1) == 0) {
            unsigned long now = millis();
            expire_mac(now, 60000);
            if (add_mac(now, addr2)) {
                sprintf(text, "%10d: ", now);
                Serial.print(text);
                print_mac(addr2);
                sprintf(text, " added: %d\n", unique_num);
                Serial.print(text);
            }
        }
    }
