I use a cheap Xiaomi LYWSD03MMC to monitor humidity. When I shower it rises up above 90%, and this only happens when showering. HA then turns on the towel rail via MQTT to an HBN wall switch. Magic!
I do the same, only mine triggers the robot vacuum 
Also using the humidity sensor is pretty quick once you turn on the shower!
I’ve resolved this issue by sticking an aquara vibration sensor under my bathtub. The light goes off only if the sensor is off for a long time.
PIR (Passive InfraRed) detectors will not see through glass. The principle of the detector is that it devides the area into sectors and looks for temperaturetransfer between sectors. If You want the detector to recognize You throug the glass You need a Microwave detector, or You sholud install an outdoor PIR in the shower (not recomended because of humidity and temperature)
Or, You could set the “ON”-time longer that the time You spend in the shower
Finally I put my homematic presence sensor at the wall to check the most of the bathroom. Also I put an hue motionsensor at the ceiling above my shower.
Currently this works, but I think the hue will not work forever as it is not that “showerable” ^^
If someone wants to review or copy the node-red code, here it is:
[
{
"id": "d8e9429e.c0c8a",
"type": "tab",
"label": "Bathroom",
"disabled": false,
"info": ""
},
{
"id": "514b47c9.1c8968",
"type": "change",
"z": "d8e9429e.c0c8a",
"name": "Off (Dimmer 0)",
"rules": [
{
"t": "set",
"p": "payload",
"pt": "msg",
"to": "0",
"tot": "str"
}
],
"action": "",
"property": "",
"from": "",
"to": "",
"reg": false,
"x": 770,
"y": 400,
"wires": [
[
"5724cd2.17d4834",
"8e677dc4.9d1ea",
"b7549478.cc6ce8",
"24ac677.f01c298"
]
]
},
{
"id": "8aaa8a68.9e4518",
"type": "change",
"z": "d8e9429e.c0c8a",
"name": "Put On (Dimmer 100)",
"rules": [
{
"t": "set",
"p": "payload",
"pt": "msg",
"to": "100",
"tot": "str"
}
],
"action": "",
"property": "",
"from": "",
"to": "",
"reg": false,
"x": 770,
"y": 360,
"wires": [
[
"5724cd2.17d4834",
"8e677dc4.9d1ea",
"b7549478.cc6ce8",
"24ac677.f01c298"
]
]
},
{
"id": "5724cd2.17d4834",
"type": "mqtt out",
"z": "d8e9429e.c0c8a",
"name": "Bathroom Ceiling 1",
"topic": "Licht-BathCeil1/cmnd/Dimmer2",
"qos": "",
"retain": "",
"broker": "1f363a4e.b0a5e6",
"x": 1060,
"y": 320,
"wires": []
},
{
"id": "8e677dc4.9d1ea",
"type": "mqtt out",
"z": "d8e9429e.c0c8a",
"name": "Bathroom Ceiling2 ",
"topic": "Licht-BathCeil2/cmnd/Dimmer2",
"qos": "",
"retain": "",
"broker": "1f363a4e.b0a5e6",
"x": 1060,
"y": 360,
"wires": []
},
{
"id": "b7549478.cc6ce8",
"type": "mqtt out",
"z": "d8e9429e.c0c8a",
"name": "Right Mirror",
"topic": "Licht-BathRiMi/cmnd/Dimmer2",
"qos": "",
"retain": "",
"broker": "1f363a4e.b0a5e6",
"x": 1040,
"y": 400,
"wires": []
},
{
"id": "24ac677.f01c298",
"type": "mqtt out",
"z": "d8e9429e.c0c8a",
"name": "Left Mirror",
"topic": "Licht-BathLeMi/cmnd/Dimmer2",
"qos": "",
"retain": "",
"broker": "1f363a4e.b0a5e6",
"x": 1040,
"y": 440,
"wires": []
},
{
"id": "1be40fc8.77782",
"type": "link in",
"z": "d8e9429e.c0c8a",
"name": "",
"links": [
"eb8bd2a7.c54ec"
],
"x": 255,
"y": 380,
"wires": [
[
"35a48ecb.f8b3b2"
]
]
},
{
"id": "99c35f6f.6dcf2",
"type": "switch",
"z": "d8e9429e.c0c8a",
"name": "Switch",
"property": "payload",
"propertyType": "msg",
"rules": [
{
"t": "eq",
"v": "on",
"vt": "str"
},
{
"t": "eq",
"v": "off",
"vt": "str"
}
],
"checkall": "true",
"repair": false,
"outputs": 2,
"x": 560,
"y": 380,
"wires": [
[
"8aaa8a68.9e4518"
],
[
"514b47c9.1c8968"
]
]
},
{
"id": "35a48ecb.f8b3b2",
"type": "amazon-echo-device",
"z": "d8e9429e.c0c8a",
"name": "Bathroom",
"topic": "Bathroom",
"x": 390,
"y": 380,
"wires": [
[
"99c35f6f.6dcf2"
]
]
},
{
"id": "32c66b6.8dd7094",
"type": "server-state-changed",
"z": "d8e9429e.c0c8a",
"name": "Homematic Presence",
"server": "26eacccb.d586c4",
"version": 1,
"exposeToHomeAssistant": false,
"haConfig": [
{
"property": "name",
"value": ""
},
{
"property": "icon",
"value": ""
}
],
"entityidfilter": "binary_sensor.000c1a4998b128_presence_detection_state",
"entityidfiltertype": "exact",
"outputinitially": true,
"state_type": "habool",
"haltifstate": "",
"halt_if_type": "str",
"halt_if_compare": "is",
"outputs": 1,
"output_only_on_state_change": true,
"for": 0,
"forType": "num",
"forUnits": "minutes",
"ignorePrevStateNull": false,
"ignorePrevStateUnknown": false,
"ignorePrevStateUnavailable": false,
"ignoreCurrentStateUnknown": false,
"ignoreCurrentStateUnavailable": false,
"x": 160,
"y": 240,
"wires": [
[
"ddacbd2c.79e71"
]
]
},
{
"id": "9eb5fd3c.ab184",
"type": "server-state-changed",
"z": "d8e9429e.c0c8a",
"name": "Hue Bathroom",
"server": "26eacccb.d586c4",
"version": 1,
"exposeToHomeAssistant": false,
"haConfig": [
{
"property": "name",
"value": ""
},
{
"property": "icon",
"value": ""
}
],
"entityidfilter": "binary_sensor.hue_bathroom_motion",
"entityidfiltertype": "exact",
"outputinitially": true,
"state_type": "habool",
"haltifstate": "",
"halt_if_type": "str",
"halt_if_compare": "is",
"outputs": 1,
"output_only_on_state_change": false,
"for": 0,
"forType": "num",
"forUnits": "minutes",
"ignorePrevStateNull": false,
"ignorePrevStateUnknown": false,
"ignorePrevStateUnavailable": false,
"ignoreCurrentStateUnknown": false,
"ignoreCurrentStateUnavailable": false,
"x": 120,
"y": 180,
"wires": [
[
"ddacbd2c.79e71"
]
]
},
{
"id": "ddacbd2c.79e71",
"type": "BooleanLogicUltimate",
"z": "d8e9429e.c0c8a",
"name": "",
"filtertrue": "both",
"persist": true,
"sInitializeWith": "WaitForPayload",
"triggertopic": "trigger",
"outputtriggeredby": "all",
"inputCount": 2,
"topic": "result",
"x": 440,
"y": 220,
"wires": [
[],
[
"64c3163f.496008"
],
[]
]
},
{
"id": "64c3163f.496008",
"type": "switch",
"z": "d8e9429e.c0c8a",
"name": "",
"property": "payload",
"propertyType": "msg",
"rules": [
{
"t": "true"
},
{
"t": "false"
}
],
"checkall": "true",
"repair": false,
"outputs": 2,
"x": 650,
"y": 220,
"wires": [
[
"8aaa8a68.9e4518"
],
[
"514b47c9.1c8968"
]
]
},
{
"id": "1f363a4e.b0a5e6",
"type": "mqtt-broker",
"name": "",
"broker": "",
"port": "",
"tls": "",
"clientid": "",
"usetls": false,
"compatmode": false,
"keepalive": "60",
"cleansession": true,
"birthTopic": "",
"birthQos": "0",
"birthPayload": "",
"closeTopic": "",
"closeQos": "0",
"closePayload": "",
"willTopic": "",
"willQos": "0",
"willPayload": ""
},
{
"id": "26eacccb.d586c4",
"type": "server",
"name": "homeassistant",
"legacy": false,
"addon": true,
"rejectUnauthorizedCerts": true,
"ha_boolean": "y|yes|true|on|home|open",
"connectionDelay": false,
"cacheJson": true
}
]