A picture of a phone with a singular large green pick up button and a speaker piece. It also has volume up and down keys. The phone looks somewhat amusing, since it doesn't have a decline button, nor any other functions. It is about as large as a small tictac box. (Found in Mediamarkt in Germany)
Siemens Gigaset L410 DECT Cordless Clip
It pairs to landline phones to act as a receiver. Mostly used as an extension of a land line for, say, elderly who may have trouble getting to the phone quickly or people who work in their lawns.
My parents have this, it was pretty useful back when landlines were still used, because you could clip it to your shirt and talk to friends while doing something else like cleaning windows or something like that