Thanks to contribution of Johan Adler and Øyvind Kaurstad.

    Decode signal from Esic brand wireless thermometer/hygrometer.
  
    My sensor/transmitter units are bought at Clas Ohlson,
    product number 36-1794 (for main unit with one sensor)
    (http://www.clasohlson.se/link/m3/Product,Product.aspx?artnr=36-1794).
    Extra sensors are available as 36-1797.
    These products are manufactured by W.H. Mandolyn International Ltd.
    The sensor unit has their product ID WT450H, receiver unit WS2015H.
    All units marked as Esic brand.
    
    The signal is FM encoded with clock cycle around 2000 µs
    No level shift within the clock cycle translates to a logic 0
    One level shift within the clock cycle translates to a logic 1
    Each clock cycle begins with a level shift
    My timing constants defined below are those observed by my program
    
    +---+   +---+   +-------+       +  high
    |   |   |   |   |       |       |
    |   |   |   |   |       |       |
    +   +---+   +---+       +-------+  low
    
    ^       ^       ^       ^       ^  clock cycle
    |   1   |   1   |   0   |   0   |  translates as
    
    Each transmission is 36 bits long (i.e. 72 ms)
    
    Data is transmitted in pure binary values, NOT BCD-coded.
    
    Example transmission (House 1, Channel 1, RH 59 %, Temperature 23.5 °C)
    110000010011001110110100100110011000
    
    b00 - b03  (4 bits): Constant, 1100, probably preamble
    b04 - b07  (4 bits): House code (here: 0001 = HC 1)
    b08 - b09  (2 bits): Channel code - 1 (here 00 = CC 1)
    b10 - b12  (3 bits): Constant, 110
    b13 - b19  (7 bits): Relative humidity (here 0111011 = 59 %)
    b20 - b34 (15 bits): Temperature (see below)
    b35 - b35  (1 bit) : Parity (xor of all bits should give 0)
    
    The temperature is transmitted as (temp + 50.0) * 128,
    which equals (temp * 128) + 6400. Adding 50.0 °C makes
    all values positive, an unsigned 15 bit integer where the
    first 8 bits correspond to the whole part of the temperature
    (here 01001001, decimal 73, substract 50 = 23).
    Remaining 7 bits correspond to the fractional part.
    
    To avoid floating point calculations I store the raw temperature value
    as a signed integer in the variable esicTemp, then transform it to
    actual temperature * 10 using "esicTemp = (esicTemp - 6400) * 10 / 128",
    where 6400 is the added 50 times 128.
    When reporting the temperature I simply print "esicTemp / 10" (integer division,
    no fraction), followed by a decimal point and "esicTemp % 10" (remainder, which
    equals first fractional decimal digit).
    
    Summary of bit fields:
    1100 0001 00 110 0111011 010010011001100 0
     c1   hc  cc  c2    rh          t        p
     
    c1, c2 = constant field 1 and 2
    hc, cc = house code and channel code
    rh, t  = relative humidity, temperature
    p      = parity bit
    
    Main decoding was done by Øyvind Kaurstad (http://personal.dynator.no/),
    who reported about his work back in 2006 at
    http://www.varmepumpsforum.com/vpforum/index.php?topic=3145.msg101023#msg101023
    (Swedish forum, Øyvind writes in Norwegian).
    On my request he let me share his findings (a spreadsheet analyzing signals
    as captured by a digital oscilloscope), which made it quite easy for me to
    write the actual code that decodes the wireless signal I receive.