Thank you for the input. I´ll consider it and the maybe hide it on top of the wardrobe or something.
Meanwhile I flashed my second gateway and while it is still connected with UART I connected a smoke detector. Thereafter I send a “Test Alert” from the Xiaomi App to the Detector which then creates a “beep” on the detector. So the gateway is able to send commands to the detector. It´s a question of how, I guess. Here is what I tracked with putty. Maybe someone has more expertise and can use it and in future solve the problem. I replaced my device ID with “MYDEVICEID”
###set_device_prop={“from”:“4”,“id”:36,“method”:“set_device_prop”,“params”:{“sid”:“lumi.MYDEVICEID”,“write_info”:50397184}},time=1439420
01-31 22:59:50.431
{“id”:87,“sid”:“lumi.MYDEVICEID”,“model”:“lumi.sensor_smoke.v1”,“method”:“event.self_check”,“params”:}
01-31 22:59:50.441
{“id”:88,“sid”:“lumi.MYDEVICEID”,“model”:“lumi.sensor_smoke.v1”,“method”:“props”,“params”:{“device_log”:“[1580482789,["event.self_check",]]”}}
###set_device_prop={“from”:“4”,“id”:38,“method”:“set_device_prop”,“params”:{“sid”:“lumi.MYDEVICEID”,“write_info”:50397184}},time=1441056
###set_device_prop={“from”:“4”,“id”:40,“method”:“set_device_prop”,“params”:{“sid”:“lumi.MYDEVICEID”,“write_info”:50397184}},time=1442696
###set_device_prop={“from”:“4”,“id”:42,“method”:“set_device_prop”,“params”:{“sid”:“lumi.MYDEVICEID”,“write_info”:50397184}},time=1444251
##SmokeGas write,time=1444263
=eSL_WriteMessage= t=0110,l=19,data= 07 1d 56 01 01 05 00 00 01 11 5f 01 23 ff f1 03 01 00 00
LOG:write u8Status=0
=recv zigbee message:Free=167624 ,t=9f96;l=5;data= 00 21 01 10 05
=eSL_WriteMessage= t=0010,l=0,data=
=eSL_WriteMessage= t=9f0a,l=0,data=
=recv zigbee message:Free=167872 ,t=8010;l=6;data= 56 31 2e 35 38 00
=recv zigbee message:Free=167872 ,t=8000;l=5;data= 00 00 00 10 00
=recv zigbee message:Free=167872 ,t=9f8a;l=1;data= 1f
zigbee temperature is:31
=recv zigbee message:Free=167872 ,t=8000;l=5;data= 00 00 9f 0a 00
###set_device_prop={“from”:“4”,“id”:44,“method”:“set_device_prop”,“params”:{“sid”:“lumi.MYDEVICEID”,“write_info”:50397184}},time=1445866
##SmokeGas write,time=1450284
=eSL_WriteMessage= t=0110,l=19,data= 07 1d 56 01 01 05 00 00 01 11 5f 01 23 ff f1 03 01 00 00
LOG:write u8Status=0
=recv zigbee message:Free=168120 ,t=9f96;l=5;data= 00 22 01 10 06
=recv zigbee message:Free=168120 ,t=8702;l=7;data= f0 21 01 01 02 1d 56
=recv zigbee message:Free=168120 ,t=8110;l=8;data= 06 22 1d 56 05 00 01 00
01-31 23:00:07.070
{“id”:89,“sid”:“lumi.MYDEVICEID”,“model”:“lumi.sensor_smoke.v1”,“method”:“props”,“params”:{“write_info”:50397184}}
###set_device_prop={“from”:“4”,“id”:46,“method”:“set_device_prop”,“params”:{“sid”:“lumi.MYDEVICEID”,“write_info”:50397184}},time=1462609
01-31 23:00:13.621
{“id”:90,“sid”:“lumi.MYDEVICEID”,“model”:“lumi.sensor_smoke.v1”,“method”:“event.self_check”,“params”:}
01-31 23:00:13.630
{“id”:91,“sid”:“lumi.MYDEVICEID”,“model”:“lumi.sensor_smoke.v1”,“method”:“props”,“params”:{“device_log”:“[1580482812,["event.self_check",]]”}}
##SmokeGas write,time=1463304
=eSL_WriteMessage= t=0110,l=19,data= 07 1d 56 01 01 05 00 00 01 11 5f 01 23 ff f1 03 01 00 00
LOG:write u8Status=0
=recv zigbee message:Free=167352 ,t=9f96;l=5;data= 00 23 01 10 07
###set_device_prop={“from”:“4”,“id”:48,“method”:“set_device_prop”,“params”:{“sid”:“lumi.MYDEVICEID”,“write_info”:50397184}},time=1465668