That works well if you have a basic ON/OFF fan and I’m using these (and similar) for other devices. But what I’m talking about is Wahoo HEADWIND. It is fairly powerful and so to control the air it has 4 different fan speed settings. While the option to control the fan speed by your Heart Rate or Speed BLE sensors is already available and works great, in practice it’s more like a gimmick as both are not precisely tied to the actual cooling needs. There are rest/cold days when speed setting nr 2 makes me too cold and intense/hot days when speed setting nr 4 is just about right. Also, the demand changes - in the warmup I want it lower, during the race/workout I want it at max.
So basically my problem is not ON/OFF before/after ride, but more like ON-1-2-3-4-OFF that changes during the ride
You can do all that in Wahoo app, which is OK. In practice I would rather have an option to either build my own sensors/automations to control the fan speed (think advanced power/temperature/humidity logic, or even something predictive based on workout profile), or make a remote/panel with big +/- or 1-4 buttons so I can control the fan remotely and easily, rather than picking up the phone, opening app, waiting for device to find sensors and then change setting. That’s a bit of a pain during efforts. Yes, I could probably make a “fake” HR sensor sending arbitrary HR values based on my actual needs, pair it with HEADWIND and control it that way, but it seems unnecessary when all I need technically is to set a value of one BLE characteristic.