I have a Gigaset cordless phone in the workshop. Just the one handset, base station plugged into the landline.
A few times recently - including last night at about midnight, it has rung. But not the normal ring. And no other phones in the house on the same line ringing.
The ring is odd - a sort of musical jingle like it was played from a tape running backwards. Sort of fades in, and cuts off abruptly. Then repeats. Goes on for about 30 seconds. Display reads new message. But no way of reading it.